128 Analysis of Scientific Books. 
10. An Account of Experiments made with an Invariable Pendu- 
lum at New South Wales. By Major-General Sir Thomas Bris 
bane, K.C.B. F.R.S. 
[Communicated by Captain Henry Kater, F.RS., in a Letter addressed to 
Sir H. Davy, Bart., P.R.S.] 
The results of Sir Thomas Brisbane’s experiments are as follow: 
39-07696 inches the length of the pendulum, vibrating seconds at 
Paramatta; .0052704 the diminution of gravity from the pole to 
the equator, and -->+,— the resulting compression. 
11. Observations and Experiments on the daily Variation of the 
Horizontal and Dipping Needles under a reduced directive Power. 
By Peter Barlow, Esq., F.R.S., of the Royal Military Academy. 
{Communicated by Davies GiLvert, Esq., V.P.R.S.] 
The daily change of the horizontal needle is so small, that it has 
only hitherto been detected with the most careful observations, and 
with the most delicate instruments; and in the dipping needle, that 
change is so extremely minute, as to have escaped observation al- 
together. It occurred to Mr. Barlow, that it would be possible to 
increase this deviation in both needles, so as to render it distinctly 
observable, by reducing the directive power of the needle, by 
means of one or two magnets properly disposed, to mask, at least 
in part, the terrestrial influence. This idea was realized, and in 
this way it is easy to produce a daily variation, to almost an 
amount. From his experiments, Mr. Barlow draws the following 
conclusions :— 
1st. That while the north end of the needle is directed to any 
point from the south to N.N.W. its motion during the forenoon is 
towards the left hand, advancing to some point between the N.N.W. 
and north; and while it is directed towards any point between the 
north and S.S.E., it passes to the right hand, that is, still to some 
point between the north and N.N.W. 
2dly. That the daily change is not produced by a general de- 
flection of the directive power of the earth, but by an increase and 
decrease of attraction, of some point situated between the north 
and N.N.W., or between the south and S.S.E. 
3dly. That the dipping needle is subject to a daily variation, 
which cannot, at present, be reduced to any fixed principles. 
12. On the Diurnal Deviations of the Horizontal Needle when un- 
der the influence of Magnets. By Samuel Hunter Christie, Esq., 
M.A., Fellow of the Cambridge Philosophical Society: of the 
Royal Military Academy. 
[Communicated by Sir H. Davy, Bart., P.R.S.] 
Mr. Barlow communicated to Mr. Christie his method of ren- 
