146 
Analyses of Books. 
of the needles, and over the centre of which, the silk fibre was suspended. The bot. 
tom of the box, being rendered horizontal, by means of foot screws ; and shown 
to be so, by an attached spirit level : the zeros of the circle, were placed in the di- 
rection of the magnetic meridian ; and a needle was suspended in a horizontal posi - 
tion. Another needle was then employed, to draw it 50 or 60 degrees from its na- 
tural dilection ; on the removal of which, the suspended needle resumed its direc- 
tion, in the ordinary process of vibration. The registry of the vibrations was com- 
menced when the arc had diminished .to 30°, and continued, until it was reduced 
to below 5° ;the method of registering the vibration will be best understood, by a re- 
ference to the dose, and is too simple to require further explanation. The num- 
ber of vibrations made by each needle, between the arcs of 30°, and 5°. was usually 
from 300 to 400, and the times in which these were performed, varied, in the dif- 
ferent needles, from 12 to 16 minutes; the mean time of performing 100 vibrations, 
between the specified arcs, is the result deduced for each experiment.” 
The results by different needles -were as follows : Supposing the intensity at 
London to be 1, it was found to be at Paris 
1.0732 
1.0675 
1.0726 
1.0723 
1.0709 
1.0717 
Mean 1.07137 
“ From the very careful observations which are regularly made, on the dip of 
the needle, at the Royal observatory at Paris ; the mean dip, corresponding to the 
period when these experiments were made, is known to have been 67 0 .58". In as- 
suming the dip, at the same time in London, to have been 69°.45' (which is allowing 
a diminution of 3', per annum, since it was observed in 1621 to be 70°.04' (Ph. Tr. 
1822 Art. 1) we cannot fail to be sufficiently near the truth, for the present pur- 
pose. The horizontal intensity at Paris, being then as 1,0714 to 1 at London ; it 
results, that the absolute intensity of terrestrial magnetism, was greater at London, 
than at Paris, at the period of these experiments by about 11 parts in 1000.” 
“ The horizontal intensity at Loudon and Edinburgh, were as 1 : 0,9505.” 
II. On the resistance of fluids to bodies passing through them. By James Walker, 
Esq. F. R. S. E. communicated by Davis Gilbert, Esq. M. P. V. P. R. S. vr • 
13 to 23. 
This paper we shall reprint at length in our next number. 
III. On the corrections in the Elements o/DeLambre’s Solar Tables required by 
the observations made at the Royal Observatory, Greenwich. By George Biddel 
Airy, Esq. M. A. Fellow of Trinity College, Cambridge, and Lucasian Professor of 
Mathematics m the University of Cambridge; communicated by John Frederic Wil- 
liam Herschel, Esq. V. P. R. S. pp. 23. to 34. 
This appears to be a valuable paper, but scarcely capable of abridgment. Mr. 
Airy object was to compare a series of 10 years’ observations of the sun’s right 
ascension ; with his place as determined by calculation, from the tables of DeLam- 
bre. He finds the following corrections in the several elements required to make 
the calculated and observed places agree. 
“ The epoch for 1821,5 ought to be increased by 5”, 061.” 
“ The e P<>ch of the perigee ought to be increased by 46", 3. These epochs are to 
be measured from the equinoxial point, adopted by Mr. Pond, in his catalogue of 
loJo. 
** The greatest equation of the centre ought to be diminished by 0",84” 
ct The mass of Venus ought to be reduced in the proportion of 10000 to 8911 or 
9 : 8 nearly.” 
“ The mass of Mars ought to be reduced in the proportion of 10000 to 6813 or 
22 : 15 nearly.” 
“ The coefficient of the lunar equation ought to be diminished by 1 "04. The 
coefficient in DeLambre’s tables is 7, "5 ; hence, if the Moon’s parallax be not altered, 
the quotient of the Moon’s mass by the sum of the Moon’s and Earth’s masses is to 
be diminished in the ratio of 29 : 25 nearly. 
If these deductions could be relied on, we should have 
Mass of Venus= 457211 X that of the sun, 
Mass of Mars= 3735552 X that of the sun, 
