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XV. Proceedings of Learned Societies. 
ASTRONOMICAL SOCIETY OF LONDON. 
Jan. 1.—A PaPER was read “On the Theory of Astro- 
nomical Instruments” by B. Gompertz, Esq. wherein the author, 
after stating the respective provinces of the practice and theory 
in relation to the construction of astronomical instruments, pro 
ceeds to divide them into two classes: viz. those constructed ac- 
cording to the best rules of the art, which he proposes to call 
instruments formed by direct construction; whilst others of in- 
ferior merit, and whose formation is not so perfect. he proposes 
to call instruments formed by inverse construction. 'The ob- 
ject of the paper is to examine the results which may be pro- 
duced by instruments of the datfer kind ; and to show that, pro- 
vided they are strong, and the parts, not intended for motion 
well fixed, a proper application of theory and observation will 
nevertheless enable the astronomer to obtain accurate results. 
His method is illustrated by several formule and examples. 
A notice was also communicated from Mr. Bowdich, re- 
specting some errors which appear to have crept into Mr. Park’s 
calculations of the latitudes of several places in Africa. These 
errors seem to have arisen from Mr. Park having madvertently 
reckoned on the month of April as having thirty ove days; in 
consequence of which all his subsequent dates were incorrect. 
And when the declinations of the sun and moon were taken 
from the Nautical Almanac, for the purpose of computation, 
they were taken out for the wrong day. Mr. Bowdich gives a 
~table of the corrected latitudes of upwards of twenty places; the 
differences of which vary from 1’ to 55’ from Mr. Park’s caleu- 
lations. 
A paper was also read ‘on the collimation-adjustment of a 
transit instrument by circumpolar stars,” by J. South, Esq. in 
which the author, after some remarks on the several modes of 
adjusting the collimation of a transit instrument, proposes the 
observation of certain circumpolar stars, whose slow motion 
renders them applicable to this purpose. He directs the instru- 
ment to one of these stars, when nearly on the meridian, and 
notes its transit over the first, second, and third wires: then, 
reversing the instrument, he notes its transit over the fourth and 
fifth wires; which are in fact the first and second wires already 
alluded to; and consequently the error of collimation (if any) is 
detected by a comparison of the intervals of time. ‘The author 
then points out several advantages attending this plan; and 
suggests the propriety of adding a few more of such cireumpolar 
stars to our fundamental catalogue, in order that their use, in 
this respect, may become more general. 
XVI. In- 
