SCIENTIFIC SUMMARY. 
287 
t = 3 - 0748 seconds; 
or 
g = 979’58 centimetres per second per second in air, 
or 
g — 979*74 centimetres 'per second per second in vacuo for the Imperial 
College of Engineering , Japan — 
a result agreeing extremely closely with the number 979‘7 obtained from 
Clairault’s formula. 
In beginning this series of observations it was expected to find g to be 
greater than Clairault’s formula gives it. Clairault’s formula assumes a 
circular equator ; Capt. Clarke has found that the equator is elliptical, one 
extremity of its major axis being in 15° 34' E. longitude ; and therefore 
Tokio is in longitude nearer a minor axis than a major one. There may be, 
however, a reason why g satisfies so well Clairault’s formula, in spite of this 
excentricity of the equator. The greatest depression of the Earth’s surface is 
only a few hundred miles to the east of Japan ; and probably the diminution 
in g produced by this cause just counter-balances the increase of g produced 
by ehipticity of the equator. As for local perturbations, it is to be remarked 
that Tokio is situated on a very large plain, there being no hills of any 
magnitude within eighty miles. The geodesy of Japan is of special interest 
on account of the great Pacific depression, and on account of the very gradual 
slope of the earth’s surface from Japan to China, which causes Japan to be a 
sort of ridge. 
On the Dynamo-electric Current is the title of a paper read before the 
Royal Society by M. Siemens. He points out that the Gramme and Siemens 
machines are both subject to the drawback that an increase of external 
resistance causes a falling-off of the current, and that, on the other hand, 
short-circuiting the outer resistance, through contact between the carbons of 
the lamp, much increases the electric excitement of the machine, and the 
power necessary to maintain its motion, giving rise to rapid heating, and to 
destructive sparks in the machine itself. An observation in a paper of 
Wheatstone’s is referred to, showing that a powerful current is set up in 
the shunt-circuit of a dynamo-electric machine, which has been since taken 
advantage of in the Ladd and Brush machines as a current-generator. 
The chief object of this paper is to show how machines worked on the 
shunt system can be made to give maximum results. It seems that the 
resistance on the rotating helix has to be greatly reduced, by increasing the 
thickness of wire employed, and that on the magnets increased more than 
tenfold, by increasing the length and weight of coil-wire employed. The 
results are thus summarized, — 
1. The E.M.F. increases at first rapidly with increased resistance, and 
then more slowly towards an asymptote. 
2. The current in the outer circuit is actually greater for a unit and a- 
half resistance than for one unit. 
3. With external resistance of one unit, about equivalent to an arc 
through which 30 to 40 Webers are passing, 2 44 horse-power is expended, 
of which 1*29 is useful, giving an efficiency of 53 per cent as compared with 
45 per cent of the ordinary machine. 
4. The maximum energy which can be demanded from the engine 
