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July 5. 3 62 3 5.4 - 1.36 3 4.84 3 4.04 July 8. 3 1.4 3 3.6

§

1:31 3 7.09 3 2.29 6. 5.3 6.7 -1.35 3.95 5.35

9. 3.6 4.2 -].30 2.30 2.90 9. 6.0 4.9 - 1:31 4.69 3:59

10. 3.5 3.3 -1.28 2.22 2.02 15. 5.5 5.5 -1.18 4.32 4:32

11. 3•7 3.0 -1.27 2.43 1.76 16. 5.9 5.7 - 1.15 4.75 4.55

12. 3.1 3.0 - 1.24 1.86 1•76 22. 4.8 5.3 -1.04 3.76

4.26

14. 2.7 2.4 -1.21 1.49 1:19 23. 4.5 5.9 - 1.01 3.49 4.89

15. 3.3 3.0 - 1.20 2:10 1.80 25. 5.1 5.4 -0.98 4.12 4.42

16. 1.9 3.8 -1•19 0.71 2.61 26. 6.0 5.6 -0.95 5.05 4.65 17. 3.8 2.4 -1.17 2.63 1.23 27. 57 5.6 -0.94 4.76 4.66

21. 2.7 2.1 - 1.08 1.62 1:02 29. 4.9 5.9 -0.89 4:01 5.01

22.
4.3 3.0 - 1.04

3.26 1.96 31. 4.6 4.0 -0.84 3.76 3:16

24. 3.3 3.6 -1.01 2.29 2:59 August 1.

3.8
4.7 -0.81 2.99 3.89

25. 3.2 2.6 -0.98 2.22 1.62 3. 4.8 4.9 -0.77 4:03 4.13

30.
3.2

3.1 -0.86 2:34 2.24 4. 6.0 5•2 -0.74 5•26 4.46 August 2

2.3 3.4 - 0.84

1.46 1.96 6. 4.8 4.0 -0.69 4:11 3:31

6. 2-3 1.8 -0.71 1:59 0.21 9. 5.1 4.8 -0.61 4.49 4.19

ll. 3.6 2-6 -0.55 3:05 2:05 11. 2:9 4.7 -0.56 2:34 4:14

12. 2.4 1.3 -0.52 1.88 0.78 13. 3.6 5.4 -0.50 3.10 4.90

16. 2.5 1.0 -0.43 2:07 0:57 14. 4.1 4.6 -0.47 3.63 4:13

19.

3:1 1.6 - 0.32 2.78 1.28 16. 3.0 4.3 -0.42 2.58 3.88

2.0 2-3 -0.24 1.76 2:06 2.1. 3.7 4.6 -0.19 3:51 4.41 23. 2.0 3.0 -0.21 1.79

2.79 25. 3.6 3.9 -0.13 3.47 3.77

25. 1.4 2.0 -0.15 1.25 1.86 26. 3.9 4.2 -0.09 3.81 4:11

27.

2.3 2.1 -0.08 2.22 2.02 27.

4.5 4.4 -0.06 4.44 4.34 Sept. 5. 1.0 1.9 +0.24 1.24 2.14 28. 4.7 4.7 -0.04 4.66 4.66

12. 1.4 1.7 +0.45 1.85 2:15 Sept. 1. 3.0 3.6 +0:10 3:10 3.70

13.
1.1

207 +0:49 1:59 3:19 3. 1.6 3.7 +0.16 1.76 3.86

15. 1.3 0•4 +0:57 1.87 1.97 4. 3.6

3.9 +0.19 3.79 4:09 16. 0.8 1.2 +0.60 1.40 1.80 5. 2.8 37 +0.23 3.03 3.93 6. 3.5 4.3 +0.26 3.76 4.56 12. 2.7 3.9 +0.43 3•13 4.33 18. 2.8 3.0 +0.67 3.47 3.67 20.

2.6 3.7 +0.75 3:35 4.45 23. 3•1 3.3 +0.86 3.96 4:16

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Mean of 70 obs. (= 35 x 2) with both circles for the epoch Jan. 1, 1833, as above =
Sum of Annual Variations of both stars

3 4.018

2.240

Difference of North Polar Distance reduced to Jan. 1, 1834, by 70 obs. in 1833
Mean of 58 obs. (= 29 x 2) for Jan. 1, 1834, by 58 obs. in 1834 ...

3 1.778
3 1.877

Mean of total 128 obs. Jan. 1, 1834 ...

3 1.823

TABLE IV.

Fundamental determinations of the Zenith Distances of y Draconis.

Observed
State of zenith dist.

lunar reduced Epochs.

nuta- to the be.
tion. ginning of

Zenith distance deduced from M. BESSEL's

Difference Side Formula (TABULÆ REGIOMONTANÆ, p. 46.). of formula of

and ob

served zen.
Epochs.

Resulting
Ist term. 2nd term.
1800.

dist.
Z. D.

zen.

each year.

1753. -"6-87 2.05 N. 26-669 +33-555 +2.2333 2.457 +6.407 By BRADLEY with Zen. Sector. 1768. + 3.832 50•30 2 26.669 +22.899 +1.035 2 50.603 +0•303 MASKELYNE Ditto. 1802. +9.522 25.30 2 26.669 1.428 +0.004 2 25.245 -0.055 Ditto.

Ditto. 1813. – 7.64 2 17.40 2 26.669 9.281 +0.171 2 17.559 +0:159

POND

Ditto. 1833. - 4:30 22:47 12 26.669 - 23.560 +1.101 2 4.210 +1.740

Ditto New Zen. Telescope.

The above results (column 3rd) are those that have been obtained with the greatest care during their respective periods; and having been deduced from observations with the zenith sector, they are quite independent of the latitude of the Observatory.

M. Bessel's formula is deduced from the observations for the first sixty years, and therefore agree very well; but when we attempt to predict from the observations of these sixty years the place of the stars for twenty years to come, we find a difference of 1":74 between the predicted and observed zenith distance, the observed place being this quantity south of it.

Explanation of the foregoing Tables. Table I. contains the results of 60 observations of the small star Bode 170 Draconis, made with Jones's circle, and is intended to show what degree of accuracy may be obtained by extreme care. The mean difference 0":357, column 3, between the mean of the wbole and each result, (and which is nearly the probable error of a single observation from this series,) denonstrates with what care they have been made. The same may be said with respect to the mean difference of column 4, namely, 0":155, which is similarly obtained from the mean of the whole and the mean of each ten (a quantity which represents nearly the probable error of the mean of ten observations). However, it may be remarked, that the exact coincidence exhibited throughout this series does not prove the truth of the final north polar distance of the star here assigned, since some omissions or errors in the process of reduction would affect it. That no instrumental error exists is demonstrated by the identity of the result with that obtained with the new instrument.

Table II. contains the same observations arranged in a different manner.

This is the arrangement I have advantageously followed in investigating the difference of parallax; the object being to distinguish the effect arising from accidental error of observation from that which is due to any permanent astronomical cause.

This method should be employed when the object is to judge of the consistency of observations, without any reference to the astronomical result.

Table III. shows the manner in which the difference in zenith distance between the two stars is obtained by means of the circles ; a quantity, as I have shown, of the highest importance in the investigation.

This quantity, having been determined by the microscopes of the respective circles, might be erroneous if the runs of the microscopes were not exact, although the error here must be very small, twelve microscopes being constantly used. But as they have lately been taken down, examined, and replaced, without any sensible alteration, it may be presumed that the error from this source is sufficiently corrected.

Table IV. This Table contains in a very compressed form the result of an immense number of observations of y Draconis during a period of eighty years; and it will be seen that if from M. Bessel's formula*, deduced from the first sixty years of these observations, we attempt to predict or assign the place of the star for the present time or twenty years in advance, the star will be found 1"-75 south of its computed place.

و

* By this formula the zenith distance of the star north for 1800, + t = 2' 26":669 – 7.0":71394 + 12. 0":001011. Where t is the number of years before or after 1800, if before, the sign of t is minus.

IX. Some account of the Eruption of Vesuvius, which occurred in the month of August

1834, extracted from the Manuscript Notes of the Cavaliere MONTICELLI, Foreign Member of the Geological Society, and from other sources; together with a Statement of the Products of the Eruption, and of the condition of the Volcano subsequently to it. By Charles Daubeny, M.D. F.R.S. F.G.S. &c., Professor of Chemistry and Botany in the University of Oxford.

Received February 25,-Read March 19, 1835.

THE eruption of Vesuvius which occurred in the month of August of last year, excited on the spot an unusual share of interest, from the largeness of the volume of lava at the time discharged, and the extent of the damage it occasioned in its progress down the mountain ; whilst in a scientific point of view it attracted the greater attention, since it was regarded by many as the concluding link in a series of volcanic operations, which had been going on up to that period with only occasional intermissions from the year 1831.

It was therefore natural, that on my arrival at Naples shortly after the mountain had subsided into a state of comparative repose, I should seize upon the opportunity which appeared to offer of increasing my acquaintance with volcanic phenomena; first, by collecting on the spot such information as could be best relied on, with respect to the leading features of the past eruption; and secondly, by ascertaining from personal examination the actual condition of the volcano, and the products resulting either from its late operations, or from those in actual progress.

With a view to the former object, I solicited and obtained from the Cavaliere MONTICELLI (one of the Foreign Members of the Geological Society) a written account of the eruption, from which he has permitted me to extract such particulars as I might deem likely to interest the Members of the Royal Society; whilst in the hope of accomplishing the latter object, a considerable portion of the time I spent at Naples was taken up in visiting the several parts of Vesuvius, and in collecting the solid as well as aeriform substances, ejected from its crater, and from the recently erupted lava.

In the former part, therefore, of the present communication, I can claim no further sbare, than as the compiler of facts observed and reported to me by others; and all that I conceive myself personally responsible for is the latter portion, in which I have stated the several products and actual condition of the volcano at the time I visited it.

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