siciens in general; for, independent of other important considerations, it is intimately connected with the determination of the law that regulates the distribution of heat over different climates; and it is only by obtaining the mean temperature of a place at different and distant periods, that the great question can ever be solved, as to whether the temperature of this country, or of the globe in general, is increasing, stationary, or diminishing.

Ordinary thermometers, it is well known, give the temperature of the atmosphere at the moment of observation only; there are others contrived to indicate the maximum and minimum temperatures which may have occurred between any two selected epochs,-but no instrument has yet been constructed which would accurately ascertain, and register, the mean temperature of the periods between two such epochs, however short it might be.

A skilful timepiece-maker of Copenhagen, M. Jules Jurgensen, eminent for the excellence of his chronometers, and for a Treatise on Detached Escapements, has succeeded in an attempt to produce such an instrument. It is, in fact, by means of chronometers that he exhibits the mean temperature desired *. It is generally known that, to prevent variations of temperature affecting the going of a watch, there is attached to the balance-wheel of good instruments a curved bar, composed of two metals, the unequal dilatation and contraction of which, under the same temperature, shortens and extends the curve, and thus accelerates or retards the motion.

* In the Edinburgh Encyclopædia, Art. Atmospherical Clock, a machine is stated to have been proposed by Dr. Brewster, which should record any variation of temperature that takes place during a given period, and indicate on the dial-plate the exact average of all the heights of the mercury in the thermometer. The principle is, "that the variations of heat and cold affect the pendulum, which may be either of the tubular or gridiron kind, and which is so constructed as to render sensible, in the motion of the clock, the alternate contractions and dilatations which it undergoes." merous inquiries as to the actual existence of this instrument, we have never been able to give a satisfactory answer. A full description was promised to be given in a subsequent part of the Encyclopædia,-but either this was not done, or it has eluded more than one attempt to find it.

To nu

To apply this principle to the purpose of marking mean temperatures, M. Jurgensen first reverses the arrangement of the metals in the curved bar, so that, instead of compensating for any variation of temperature, it magnifies the effect of it; he then increases this sensibility to variation by adding a second arc, and by these means he obtains a variation of 311⁄2 seconds for each degree of temperature. It may now, after a little reflection, be conceived, that if this instrument be compared, at two distant instants, with a chronometer keeping regular time, we could ascertain, by changing the differences of time into degrees, the mean actual temperature of the period. It would be necessary, of course, previously to adjust this instrument to the thermometer, so that the march of the two instruments may be uniform and comparable. In order to render these chrono-thermometers still more useful, M. Jurgensen adds, without much increasing their bulk, a metallic thermometer, which indicates present temperature, and this, by the aid of two slides upon it, is made to give also the maximum and minimum temperatures which may have occurred between any two instants of observation.

This ingenious instrument, therefore, gives, on inspection,—

1. The temperature of the present moment.

2. The maximum temperature of the period between the present moment and that of any other moment previous to it which we have selected.

3. The minimum temperature, and, 4. The mean temperature of the same period.

The principal objection that presents itself to this desirable instrument is the cost, which necessarily occurs in all cases where chronometers are required.

Indelible Writing Ink.

DURING a recent discussion in the Académie des Sciences on the merits of some paper prepared to prevent the fraudulent removal of characters written upon it, M. Dulong called to the recollection of the Academy, that a commission appointed by them had demonstrated, that the surest means of rendering written characters indelible, was to use Indian ink dissolved in water, with a slight mixture of some acid, more particularly the hydrochloric.

Parisian Mechanics' Institution.

AN Association for the instruction of artificers, &c. has been in activity in Paris for about four years, and latterly with remarkable success.

The first idea of it is said to have originated with the late celebrated geometrician, Monge. The members are, principally, students of the Ecole Polytechnique, and their benevolent and enlightened object is the rational instruction of the working classes. The following enumeration of the subjects taught will show the value and the scope of the labours of the Association.

1. The elements of arithmetic, geometry, and drawing of the human figure and ornament.

2. Descriptive geometry, its application to masonry and carpentry; mechanics, drawing of machines, physics, and chemistry.

3. Grammar, book-keeping, Hygiène (the art of preserving health).

The whole course embraces a complete system of mental instruction adapted to the classes for whom it is intended.

The members of the institution have had the satisfaction of seeing the number of workmen who avail themselves of its advantages increasing every year. During the winter of 1834-5 the courses of geometry and of grammar had never less than 200 auditors; 625 artificers were on the lists for the class of drawing. As spring advances and employment increases, a sensible diminution in the numbers is evident, but the amount of the students, even in summer, is from 900 to 1000; in the winter it is from 1400 to 1500; they are nearly all adults. The expense of the lectures, &c. has been hitherto defrayed by the members of the Association, and by grants from the Government and the municipal authorities of Paris.

Two capital Omissions in all the British

Systems of Public Instruction.

THERE are two subjects of public instruction mentioned in the preceding article, which, though evidently of the highest importance, are never taught in Great Britain; we refer to Descriptive Geometry, and Hygiène, or the preservation of health, and the prevention, not cure, of disease.

The astonishing neglect of descriptive

geometry in this country we exposed and remarked upon recently*; and, unwilling to be merely querulous complainers, we, at the same time, commenced an attempt to render, as far as may lie in our power, this delightful and extensively useful branch of science better known amongst us.

It would be a waste of time to dwell upon the vast importance of an intimate acquaintance with the means of preserving health, and of avoiding disease, to individuals and to society.

No limit can be assigned to its beneficial consequences, and yet how deplo rably deficient are all our great establishments of individual and professional education, with respect to this valuable species of knowledge! The care of the public health is absolutely abandoned, until perhaps the nose or the pocket of some influential individual is affected. If he raises the question of a nuisance, how lamentable then is the hostile array of scientific ignorance. On questions much less complicated and obscure than the effects of miasma, vapours, &c. upon the human body, there is not the slightest difficulty, in any case, of obtaining any number and weight of opinions on one side, and balancing these by an equal weight and number on the other! and so unsettled is the general mind on these subjects, that this shock of evidence, so morally lamentable, reflects no disgrace upon any party.

On a threatened visit of a dangerous epidemic, what absurdities are promulgated and adopted as infallible pre

Page 305 of the present volume.

of muriatic acid gas, precipitated weekly + Think of several millions of gallons and uninterruptedly from the summit of a of a large town! This is now, and has been lofty chimney, upon a crowded population actually for years, the case at Newcastle; happily for the survivors of the immediate neighbourhood, if there are any, it is not intended to continue much longer. A process, recently patented by Mr. Maugham, the Chemical Lecturer at the Adelaide

street Gallery, is about to be adopted at the manufactory in question. By this prois made to enter into a new combination, cess the gas, immediately on its evolution, and, instead of rushing up the chimney to vitiate a large field of atmosphere, and annoy the vicinity, it will never enter the chimney at all, but be instantaneously fixed in a saleable product, viz., chlorate of lime used in bleaching.

ventives or cures! No intelligent guide or competent adviser is at hand, and the pestilence may rage, not only without check, but with aggravated mischief, in consequence of the general ignorance. It is well when masses, as well as individuals, profit by adversity and misfortune. The effects of the cholera at Paris were severely felt, and though the attacks of that dreadful visiter no precaution known can evade, yet it is gratifying to see the authorities of Paris, roused by the terrors which it produced, sparing no cost, no labour, to remove causes supposed to be favourable to its extension. The general attention is now sensibly alive in that metropolis to the advantages of cleanliness, drainage, and ventilation, and we have little doubt that this excellent idea of teaching the principles of Hygiène to the workmen who attend this institution suggested itself at the same epoch.

It is fortunate that, though discoveries in this important science may require the united assistance of several others, and the subtlest investigation of their most intelligent cultivators, yet its practice may often be reduced to measures of mere precaution, and generally to operations of great ease and simplicity. A more popular or interesting subject could scarcely be suggested to the many able lecturers who so frequently address the numerous auditories of every class during a London winter. And let us ask, why should not a science which would so essentially and largely contribute to the happiness of all mankind, be taught from a Chair in every university and public school? What immense fields are there for its exercise in our crowded manufactories, our mines, our prisons, our ships, our over-peopled districts, indeed, in every single dwelling, and in the habits and daily life of every individual!

celebrated English botanist, Ray. It is with pleasure that we insert the following passage from the prospectus of this association :-"Ladies are eligible as members, it being well known that there are many who have devoted their attention with success to this delightful study, and whose occupations often leave them much leisure for observation and research."

Number of British Species of Plants. THE number of species of plants found in Great Britain is about 1500. This comprises all those which exist in Lapland and Sweden, with scarcely any exception. It includes about threefourths of those which grow in Germany, and about two-fifths of those of France; the southern and sea-board provinces of the latter country adding greatly to the variety of its vegetable productions.

The vicinity of London may be considered extremely rich in objects of botanical research; for of the 1500 species of plants belonging to Great Britain, about 1000 may be found within 25 miles of the metropolis. Mr. Irvine has observed 670 of them within two miles of Hampstead, and 900 within there are great inducements to the the same distance from Croydon. Thus inhabitant of this smoky city to issue from its loaded atmosphere, and pursue the delightful and healthy researches of the botanist.-IRVINE, Meeting of the Botanical Society of London, Nov. 1836.

Bored Well at Grenelle.

THE well now boring in the slaughterhouse (abattoir) of Grenelle, near Paris, had in September last been carried down to a depth of 1150 feet. When about 1000 feet deep, the temperature at the bottom of the bore was 72° Fahr.; at the surface of the ground it was 54° only.

Geological Co-operation. "Is the granite on the right bank of the Elbe, in Saxony, more recent than the chalk?" has long been a fertile source of dispute among German geologists. Dr. Cotta, who had examined the country with MM. Humboldt and Rose, has written largely upon it, but argues that, to arrive at any degree of certainty upon the subject, explorations

beneath the surface are desirable. At the late scientific meeting at Jena this proposition met with a favourable reception, and Dr. Cotta has, in consequence, undertaken, by aid of subscriptions, to make the excavations, &c. necessary to ascertain the fact. He invites the geologists of all countries to co-operate in accomplishing the work.

The objects to be obtained are,

1. To determine, by excavations and borings in the valley of Polenz, in what manner the granite is superposed upon the Grès.

2. To expose to view, on the road from Rotherwalde to Hohnstein, on the right slope of the valley of Polenz, the boundary of the granite and the grès, in order that accurate observations may then be made of their reciprocal penetration, if such exists, and of the phenomena of their contact.

3. Finally, to examine the geological circumstances of the jurassic and free-stone (quader-sandstein) strata.

Each subscriber of a conventionsthaler (about 4s. Eng.) is considered as the holder of a share; this will entitle him to a pamphlet, descriptive of the operations and their results, with engravings, and an account of the expenditure.

The cost is thus estimated: Object No. 1, from £10 to £30. £ 4 to £ 6. £20 to £30.

2,

3,

Many distinguished geologists have become subscribers; among others, MM. Humboldt, Weiss, Leonhard, Naumann, Rose, Noeggerath, &c.

Danger of Calomel. Medico-Botanical Society's subject for Gold Medal. "AMONGST the chemical preparations that have attained great celebrity is calomel, a medicine which enfeebles all the vital powers, and which may from that circumstance derive its efficacy in subduing active inflammation; but its operation is eminently injurious; and it cannot be sufficiently deplored that it should be rashly and ignorantly employed as a domestic remedy, and even as an ordinary aperient, instead of being reserved solely for those disorders which

might seem to require it, under the advice, and by the authority, of a medical practitioner. As it is frequently thus misapplied, and as fashion, which is so often synonymous with folly, has promoted its use even in the tender age of infancy, we cannot be surprised that nervous disorders are common, that bodily vigour and mental energy are impaired, and that cases of insanity have become more numerous. An eminent physician, whose experience in such cases was very extensive, and whose opinions were founded upon accurate observations, assured me that insanity had, in many instances, arisen from the injudicious employment of calomel; and such must naturally be the result, when both the mind and the body are debilitated by factitious means, when the infirmities of old age are prematurely produced, when life becomes languid, and the power no longer exists of enjoying the gifts of Providence, and of sustaining with composure the cares and vexations of our earthly pilgrimage. Under such circumstances, an infirmity may become intolerable, and the mental faculties may be disturbed, if not destroyed; but even when such lamentable consequences do not ensue, a shattered constitution, a sort of nominal existence in a melancholy and miserable state of dejection and debility, with enfeebled nerves and almost exhausted powers, may be more afflicting to the patient than a chronical disorder. It will be said, and I am ready to admit, that a mercurial preparation has not, in an equal quantity, the same action on different individuals, and that persons are more susceptible than others of its injurious effects; but this circumstance furnishes an additional argument against the unnecessary administration of such a remedy, since its power, in any particular case, can be learned only from experience, and is sometimes found to be greater than was expected or wished by the physician. So extensive is the misuse of mercurial preparations, and so injurious are their ultimate operation, that it has been most properly determined, by the Council of this Society, to offer the gold medal for the best Essay on the question, "What is the vegetable substance which could be employed with success as a substitute for mercury in the cure of syphilis, or of diseases of the liver ?"

some

It would be of extreme importance if

for those medicines which, from their potency, may be dangerous, if not fatal, when they are misapplied, and which, even when they remove a disorder, may produce permanent injury to the patient. That such substitutes may be found in some disorders, was shown in a case which came under my personal observation, of a lady to whom I was related, and who had been accustomed, for the purpose of allaying the pain arising from an internal complaint, to take opium, of which the dose was gradually increased till it amounted to a considerable quantity; but it was last discovered, though it was then too late to remedy the evils which had been thus occasioned, that the same relief was experienced from drinking soda water. Nothing

would more contribute to the advancement of medical science, to the honour of the medical profession, and to the benefit of patients, than the cure, by safe and simple means, of difficult or dangerous diseases, instead of employing, as is too frequently done, and even in cases of a different description, substances which are powerful, but poisonous, and therefore pernicious." EARL STANHOPE, Address to MedicoBotanical Society, 1836.

Great Central Heat of the Earth not alarming.

"It appears, that if there be an increase of temperature in descending, such a fact can result from nothing but a central heat, independent of existing influences.

"The discussion of the evidence of this fact must be left to the geological speculator; but we may here mention some of the results of theory, which are fitted to make less formidable the idea of having a vast abyss of incandescent matter, within the comparatively thin crust of earth on which man and his works are supported. It results from Fourier's Analysis*, that at 124 miles deep the earth may be actually incandescent, and yet that the effect of this fervid mass upon the temperature at the surface may be scarcely a perceptible fraction of a degree. The slowness with which any heating or cooling effect would take place through a solid crust, is much greater than might be supposed. If the earth, below 33 miles

*Bull, des Sci., 1820, p. 58.

Estimate of Solar Heat imparted to the Earth.

IT may be curious to contrast the effect of the heat ascending to the earth's surface, as stated in the article preceding, with that annually poured down upon it by the sun. This is estimated by Pouillet to be sufficient to melt a coat of ice, 14 metres thick, (about 46 Eng. feet,) incrusting the whole globe of the earth. Progressive Rise of a Portion of the

Bottom of the Mediterranean.

M. THEODORE VIRLET lately addressed a note to the French Académie des Sciences, in which he directs the attention of geologists to the probability of the speedy appearance of a new island in the Grecian Archipelago, in consequence of the progressive rise of a sunken solid rock (composed of trachytic obsidian ?) in the gulf of the volcano of Santorin. The following are the author's observations on this subject:-"Towards the end of the last century, at the period when Olivier visited Santorin, the fishermen of the island asserted that the bottom of the sea had recently risen considerably between the island of Little Kaïméni and the port of Thera; in fact, the soundings did not give a greater depth than fifteen to twenty fathoms, where formerly the bottom could not be reached. When Colonel Bory and the author visited the island in 1829, they were able not only to confirm the truth of Olivier's statement, but also to ascertain, by various soundings, that the rise

+ Mem. Inst. Tom. vii. p. 603.

Tom. ii. p. 704.