SCIENTIFIC SUMMARY. 
185 
deflection of the magnet are doubled by the reflection of the mirror, and that 
consequently it is not the tangents of the real angles of deflection that one 
reads on the scale, but the tangents of the doubled angles. This assumption 
may indeed be made with very small angles, but even with a deflection of 
8° the indications are already sensibly exaggerated at the ends of the scale. 
A bifilar suspension with two silk threads very close together reduced the 
erro.s to less than one hundredth of the value measured. 
Distribution of power by Electricity has formed the subject of experiments 
by M. Tresca, using a Gramme machine making 1200 revolutions per minute. 
The current was transmitted by copper-wires to carts at different distances, 
two Gramme machines being placed on the carts, and acting on a windlass 
which drove a double Brabant plough so as to make a furrow 220 metres 
long. The velocity of the plough when the circuit was 800 metres, was 
88 centimetres per second, the shaft making 1123 turns per minute; when 
the circuit was increased to 1300 metres the velocity was 70 centimetres, 
and the revolutions of the shaft 890. The effective work was estimated at 
three-horse power. 
Electrical Storage has been described by Professors Houston and Elihu 
Thomson in the Journal of the Franklin Institute. Such a process has long 
been suggested, but has failed to become of practical use, (1) from cumbrous- 
ness, owing to the large conducting surface required ; (2) from loss of energy 
due to evolution of gas during charging ; (3) lack of constancy ; (4) limited 
capacity. These defects apply to Plante’s secondary battery; the system 
they suggest consists of a saturated solution of zinc sulphate, at the bottom 
of which is placed a plate of copper connected to an insulated wire. At the 
top is placed a second copper plate, one of hard - carbon, or of some metal 
unchanged by contact with zinc sulphate solution, and less positive than 
metallic zinc. Charging of the cell so constructed is effected by passing a 
current through it from the lower to the upper plate. The current employed 
i§ that from a dynamo-electric machine, and the result is the deposition of 
metallic zinc on the upper plate, and the formation of a dense solution of 
copper sulphate overlying the lower. The cell, in fact, becomes a gravity 
battery, acting as such, till all the deposit is redissolved. 
A somewhat similar plan has been employed by Mr. C. F. Varley to dis- 
tribute time-signals, but has been superseded by Leclanche cells of large 
dimensions. It consisted of gutta-percha chambers in. high, each with a 
division of 1| in. deep in the centre ; the shallow cells thus formed being 
half filled with mercury, and connected with the mercury in the corresponding 
cell of the neighbouring chamber. The last carbons were connected to 
terminals and to the discharging wires ; the cells were filled with zinc sulphate 
and sulphuric acid. On passing a current through sixty such cells from 150 
small Daniels, amalgamated zinc was formed on one side and bisulphate of 
mercury on the other. The arrangement had a very low resistance. 
Cast-Iron Magnets are being made by M. Carrd by running a soft and 
. slightly carburetted metal in earthen crucibles. Just before pouring, 10 to 
15 per cent of steel-filings and about 1 or 1*5 of nickel with *25 per cent of 
copper ; or 2 per cent of tin and 0*5 per cent of copper, are added. It can 
then stand tempering at a cherry-red heat. 
Nature extracts from the New York Nation a marvellous account of 
