T ——————— ULA UNI KAA ee KUMALIZA 
Pore.—A Method of measuring Position of Double Stars. 148 
and firmly held there, this raises the valves VV’, and water flows up the 
glass tube G, which has previously been filled up to the zero point of the 
scale. The instant that the second star is bisected by the wire or web the 
lever is released, the valves are immediately closed, and the flow of water 
ceases. The height of the column of water is then accurately measured by 
means of the graduated scale. Then the water is allowed to escape through 
the waste-tap T", and the operation is repeated. A mean of all the observa- 
tions gives the quantity of water that flows into the glass-tube during the 
interval between the transits of the two stars. Let this quantity be 2°25 
inches. Then an observation is made, by means of a watch, of the time 
required to fill the tube, that is to say for 30 inches of water to run into it; 
let this time be 21:5 seconds. A rule of three sum shows us the time 
elapsing between the transits of the two stars :— 
EK UE Sees. 
35 5 * 21:5 t: 1:613 
1:612 seconds of time is, Meroe the interval between the transits of the 
two stars. 
Having found this interval, a simple trigonometrical Spanien gives us 
the distance between the two stars :— 
Let p = the North Polar TM zi ne sy 
= angle of position 
= angle of position of ie line j ue the stars. 
T = interval between the two transits in seconds of time. 
A= distance in seconds of arc between the two stars. 
T x 15.sinp.cosa: 
Gea 
Then A = 
sin (a — 9). 
These calculations are not very troublesome. A very little practice 
enables one to do them very rapidly. It may be as well, in conclusion, to 
give an example just to show how very little labour is really involved in this 
process, 
On April 5th, 1876, twelve oblique transits were taken of the aber 4763 
(of Brisbane’s catalogue), R.A. 14h. Om., Decl. 53° 6 S. The average 
duration of time between the transits of the component stars of the double 
over a wire inclined 78? 5/ to the meridian, was 9:61 secs. The angle of 
position had been found to be 22° 0'. Then— 
9:61 secs. L e — 14415 Log 2158814 
sin : dis 97718455 
cos | 9-314897 
cosec d 56? 5 10081000 
1:333166 
The natural number corresponding to this is 21:58. Hence the distance 
between the stars is 213 seconds of arc. This measure was taken before 
apparatus described in this paper had been made as perfect as it is at 
