508 Lieut. -Colonel A. Strange on Aluminium Bronze. 



D' 



Hence the ratio of the increase of gravity between the equator 

 and the poles, under this new arrangement, to gravity itself 

 == l( e — i m ) : an d the ratio which this increase bears to the 

 actual increase as determined by pendulum experiments 



4(i-5r8)^ 0051828 =°- 48 - 



The effect, then, would be to reduce everywhere the gain of the 

 seconds' pendulum over the rate at the equator by very nearly 

 one-half the number of beats at present observed. 



Experiment shows no sudden changes, nor any marked devia- 

 tion from a regular increase, varying as the change in the square 

 of the latitude, in the rates of the pendulum in passing from the 

 equator to the poles. Hence the excess of matter above the 

 homogeneous spheroid cannot be distributed irregularly. If we 

 suppose it distributed in exact spherical shells, as above, the 

 effect on the pendulum would be very great, and therefore very 

 perceptible. Any departure in the strata from the spherical 

 form, not towards the oblate spheroids of the fluid theory, but 

 in the opposite direction, would produce a result still more dis- 

 cordant with experiment ; whereas every approach in the distri- 

 bution towards those spheroids will bring the calculation into 

 nearer accordance with fact. No stronger testimony can well be 

 borne to the truth of the fluid arrangement, and therefore also 

 to the fluid theory, as we cannot otherwise conceive what cause 

 can have made the interior strata to bulge out at their equators. 



Calcutta, October 27, 1862. 



LXIX. On Aluminium Bronze as a Material for the Construction 

 of Astronomical and other Philosophical Instruments. By 

 Lieut.-Colonel A. Strange, F.R.A.S.* 



THE author, after referring to the astronomical and geodesical 

 instruments about to be constructed, under his superin- 

 tendence, by order of the Government, for the use of the Great 

 Trigonometrical Survey of India, and after noticing that one of 

 the points which has given him most anxiety had been the selec- 

 tion of the proper material or materials of which to construct 

 these instruments, and that his present remarks were confined to 

 the great Theodolite with a horizontal circle 3 feet in diameter, 

 and after detailing the requirements of such an instrument, 

 proceeds as follows : — 



" Such then was the problem presented for solution : to con- 

 struct an instrument with extended powers, and cast as much as 



* From the Monthly Notices of the Astronomical Society for Nov. 1862. 



