« VorigeDoorgaan »
XVII. Observation of the Winter Solstice of 1812, with the Mural
Circle at Greenwich. By John Pond, Esq. Astronomer Royal, F.R.S.
Read February 25, 1813.
The weather this year at the period of the solstice was peculiarly unfavourable for astronomical observation; however, in the course of the month, I obtained nine observations of the sun; one of these proved defective, the result of the other eight, accompanies this communication. In my observation of the summer solstice, it will be seen that I assumed the arc ZP equal 38° 31' 21"15; by subsequent observation I conceive that I have somewhat improved this quantity, which I now assume 38° 31' 21",5, as resulting from 120 observations of Polaris.
The observation of the summer solstice thus corrected will give the mean obliquity of the ecliptic for January 1, 1813, 23° 27' 51",50, and the winter solstice 23° 27' 47",35.
There can be no doubt but this small discordance might easily be reconciled by a slight modification of BRADLEY'S refractions, and perhaps ultimately it may be necessary to have recourse to this theory for its explanation; but I am unwilling to do this hastily, being now occupied in making an extensive series of observations of circumpolar stars, with a view of determining, if possible, whether BRADLEY's mean refraction does, or does not, require alteration.-As I propose making the discordance of the solstices the subject of a sepa
124 Mr. Pond's Observation of the Winter Solstice, &c.
rate paper, I shall not add any thing farther on the subject, excepting a recommendation to astronomers, to deduce their refractions from circumpolar stars altogether, and then examine the solstices with those refractions, and by no means to make the coincidence of the solstices a required proof of their accuracy.
Note. In the annexed computation the reduction to the solstice is computed from the observed right ascension of the sun, by this means the errors of the tables being avoided, observations at a considerable distance (even some weeks from the solstice) may be employed, particularly in the winter season, when the uncertainty from refraction is greater than the error which may be probably introduced into this part of the calculation.
Dec. 630,1941383 21,1 O UL 1i2 iz 34,31+ó 6,5 38 31 15,0 + 16 17,355 31,3 74 56 29,0 113 27 50,5 7 30,42 34 293 35,2 LL 112 51 44,4 6,5 15,0
16. 17,348 37,4
46,2 9 29,81 29 243 36,5 LL 113 4 14,8
15,0 16 17,5 36 10,0 28,8
50,3 1029,73 33 30 3 27,6 UL 112 37 19,5 15,0 + 16 17,630 36,8 26,5
48,0 1129,84 35 34 3 36,0 LL 113 14 49,1
15,0 16 17,725 30,3
44,2 1329,61 32 303 30,6 UL 112 51 13,0 15,0 + 16 18,0 16 41,8 28,4
49,9 1529,44 32 31 339,3 LL 113 30 39,6
15,0 16 18,1 9 43,4
50,7 3030,1045 473 26,8 UL 112 50 38,81
15,01 + 16 18,8 17 18,0
48,9 Mean of 8 Observations
74 56 27,09 113 27 48,55 O
= Nutation + 7",62 Parallax - 8",50 Lat. -0",36 =
Observations as given
by the Instrument.
Position of the Zero point, or Equation to be applied to obtain the N, P. D.
Equation to reduce the observed N, P, D, to Zenith Distance or position of the Zenith point on the Circle.
Semidiameter of the O1' greater than in the Nautical Almanack.
Reduction to the Solstice.
Solstitial Zenith Distance.
74 56 25,85 113 27 47,35
XVIII. On the Tusks of the Narwhale. By Sir Everard Home,
Read February 18, 1813.
The structure of many animals that inhabit the great Northern Ocean, is, even at this day, imperfectly known; this arises from those who have the best opportunities of making such enquiries not being fitted for them, or being too much engaged in pursuits of a different nature. Under such circumstances too much praise cannot be bestowed on the few individuals, whose zeal for science induces them to exert themselves in improving this branch of knowledge; to one of these, Mr. SCORESBY, jun. I am indebted for the means of making the following observations on the tusks of the narwhale.
Mr. Scoresby told me, a year ago, that the female narwhale had no tusks, which astonished me; and the only reply I could make to such an assertion, was to beg that he would procure me a skull, that I might be satisfied of the fact. This he promised to do, and last summer sent me the skull of a female, in which there was no appearance whatever of tusks; and as the sutures were all united, there was every reason to believe the time of having teeth had elapsed, particularly as a male skull of the same size, and in which the sutures were not equally well united, had a tusk four feet long. With such evidence before me, I was naturally led to adopt
the generally received opinion of the captains in the Greenland fishery, that the males had one tusk, and the females none; and as I imagined that I had cleared up a part of the natural history of this species of whale, which had hitherto been involved in obscurity, I proceeded to lay these observations before the Society. After I had done so, I found
, so many contradictory accounts among my friends, that I became staggered what to believe: some had seen two tusks of different lengths in the same skull, others believed they had seen two of the same length. To set the question at rest, my
friend Mr. BROWN, Librarian to Sir JOSEPH BANKS, took the trouble of collecting all the books in Sir Joseph's library, in which the subject is mentioned. In ANDERSON's Description of Iceland, Greenland, and Davis's Straits, it is mentioned that, in 1684, Dick PETERSON brought to Hamburgh the skull of a female narwhale with two tusks, the left seven feet five inches, the right seven feet long, and that this skull had ever since been preserved there, and shewn to the curious. This account is copied by several later authors.
I found also, in Tycho L. TYCHONIUS, an account, published in 1706, of.a narwhale's skull with the left tusk seven feet long, and the right imbedded and completely concealed in the substance of the skull, nine Danish inches in length. The author takes some merit, and in my opinion deservedly, for having discovered it. A drawing of it in situ is annexed.
This information set me to work in sawing the skulls in the HUNTERIAN collection, to ascertain whether they contained rudiments of tusks not yet protruded from the substance of the bone, and the result of this investigation explains, in the most satisfactory manner, every thing that I have seen