556 Progress of Science. [October, 



by him last winter in order to ascertain whether water, when put into a strong 

 vessel (a steel cylinder of great strength, and so arranged that the dilatation, 

 or expansion, of the water when cooled below + 4*1°, could be prevented), 

 would or would not remain liquid, even when exposed to a cold very consider- 

 ably below its point of congelation, in consequence of the expansion due to the 

 cooling down from below + 4'i° being prevented by the strength of the vessel 

 containing the water and stopper (steel plug) fitted thereto. The result 

 of this investigation was found to be that water remains liquid under the con- 

 ditions alluded to, even at a temperature of — 18 , but freezes instantaneously 

 as soon as the impediment caused by the resistance of the plug which herme- 

 tically closes the steel vessel, was removed, and free play was given to the expan- 

 sion of the liquid. It should be noted that the sides and bottom of the steel 

 vessel alluded to were of such great strength as to be practically unyielding. 



ELECTRICITY. 



E. Bourgoin describes a series of experiments, from which the following 

 main results may be deduced : — When the galvanic current passes through 

 acidulated water, it will be seen that, though the total effective work done by 

 each pole is the same, the quantity of acid found in each compartment at the 

 end of the experiment will be found to vary considerably. The three following 

 cases may be distinguished: — (1) The acid is accumulated regularly at 

 the positive pole ; this occurs with sulphuric, nitric, phosphoric, benzoic, 

 succinic, camphoric, &c, acids. (2) There is no loss at the positive pole ; the 

 loss is only experienced at the negative pole, since half of the electrolysed acid 

 is regenerated in the other compartment. (3) The two compartments become 

 simultaneously poorer; this occurs with lactic, tartaric, citric, and in general, 

 all the very readily oxidisable acids. 



M. Gramme, of Paris, has recently completed a magneto-electric machine 

 from which he obtains a continuous current. The principle is that of passing 

 a permanent magnet through a coil of wire constantly in one direction ; or, 

 what is virtually the same thing, keeping the magnet fixed, and causing 

 the coil to move. To effect this M. Gramme employs an annular coil of 200 

 metres of copper wire of 2 m.m. in diameter, wrapped in silk. By a multiplying 

 wheel and pinion this coil is caused to revolve between two concave armatures 

 attached to a series of permanent magnets. One of these armatures developes 

 in the circuit an induced current in one direction, whilst the other armature 

 induces a current in the opposite direction but of the same intensity. To col- 

 lect these currents two rubbing-pieces are placed in metallic contact with the 

 coil at the neutral points of the two armatures : one of these contact pieces 

 receives the positive electricity, the other the negative, becoming respectively 

 the positive and negative poles of the electro-motor. By this means and by a 

 rather complicated method of winding the wire on the coils, M. Gramme 

 obtains a perfectly continuous current, capable of decomposing water in a vol- 

 tameter, and of producing all the results obtained with the battery. Instead 

 of permanent magnets, the inventor in practice employs electro-magnets. In 

 the latter case there is always sufficient residual magnetism to induce a 

 current in the annular coil when motion is imparted, and as in Siemens's and 

 in Wheatstone's instruments this weak current speedily induces a stronger, 

 a maximum of 700 or 800 revolutions per minute can be attained. With a half- 

 horse power, nearly 20 inches of platinum wire one millimetre diameter can be 

 heated to incandescence. The machine will be very useful where a constant 

 current of high intensity is required. 



Electricity certainly seems to be entering into nearly all sciences. Sir 

 Charles Wheatstone has at length called in its aid to Hygrometry. A thermo- 

 pile of five couples has the faces exposed in an ebonite dish in which water or 

 spirit is placed. The reverse faces of the pile are exposed to the air, insulated 

 in solid paraffin ; two connecting wires are carried to a delicate galvanometer 

 of a few turns. The variations in deflection of the needle of the galvanometer 

 thus become a relative measure of the evaporation of the liquid contained in 

 the ebonite cup, and by this means very great accuracy can be attained, as the 



