Intelligence and Miscellaneous Articles. 159 



apparatus for the reception of waves of light of medium length is 

 more liable to be overstrained by nervous shocks or by prolonged 

 excitation than is the case with those designed for the reception of 

 waves of greater or lesser length. Nervous derangement and pro- 

 longed excitation are, then, causes which may produce temporary 

 green colour-blindness. — Silliman's American Journal, Jan. 1877. 



ON SOME EFFECTS OF HEAT UPON VOLTAIC CIRCUITS COMPLETED 

 BY AN ELECTROLYTE. BY W. HELLESEN OF COPENHAGEN. 



I. It is known, and M. du Moncel has demonstrated in several 

 ways*, that if one of the plates of an electrolyte be heated, a ther- 

 moelectric action is produced, which has the effect of producing a 

 current, the heated plate constituting the positive pole. This 

 action, which often shows itself in aerial telegraphic circuits t, may 

 become very energetic if the electrolytic system be disposed so as 

 to maintain the liquid around the two plates at considerably differ- 

 ent temperatures ; and to obtain this result, we need only isolate 

 from one another the portions of the liquid into which the elec- 

 trodes dip — or to take advantage of the property possessed by all 

 liquids, of keeping at their surface the most heated portions, which 

 thus, in some measure, float upon the cool portions. To effect this 

 disposition, the electrolytic system may be constituted by two test- 

 tubes of glass, joined near their apertures by a tube of some cen- 

 tims. length, and having fixed in them the two electrodes, one at 

 the top, and the other at the bottom. In this way, when the appa- 

 ratus is filled with liquid, one of the electrodes dips into the part 

 near the surface of the liquid, the other into the opposite part ; and 

 the liquid being confined in two receivers communicating only 

 through the tube which joins them, may present in each test-tube a 

 very different temperature. In these conditions, if we take for the 

 liquid a saturated solution of sulphate of copper, and copper plates 

 for electrodes, on heating with a spirit-lamp the test-tube of which 

 the electrode occupies the upper part, we obtain a relatively ener- 

 getic current, which can be ascertained with not very sensitive rheo- 

 meters ; and the electrode, thus heated through the intermediation 

 of the liquid, becomes promptly covered with a deposit of copper. 



The experiment is also successful on employing as electrodes 

 platinum and lead, and water acidulated with sulphuric acid as the 

 electrolytic conductor. The above arrangement, however, with me- 

 tallic electrodes that are good conductors of heat, such as plates of 

 copper, and a solution of sulphate of copper, may be considerably 

 simplified. It then suffices to fix on the brim of the vessel filled 

 with this solution one of the copper plates, which must be bent so 

 as to touch with one end the surface of the liquid, and to present 

 at the other, outside the vessel, a sufficiently large surface to be 

 heated. On immersing the other plate to the bottom of the vessel 

 and uniting it to the first by a wire covered with gutta percha or 

 caoutchouc, we obtain by heating this first plate a current almost 

 as powerful as with the other arrangement. 



* See Comptes Rendus, 1872, t. lxxv. pp. 958, 1100, 1504. 

 t Ibid. pp. 958, 1623. 



