1867.] ; Physics. 437 



which the armature is made to rotate, which is entirely dependent 

 on the amount of dynamic force employed. The great improve- 

 ment in tins machine is the introduction of the second armature, 

 winch, although it takes off currents generated in its wire by the 

 increased magnetism, does not at all interfere with the primary 

 current; and when attached to a regulator is found to give an 

 electric light equal to forty elements of Grove's or Bunsen's at the 

 expenditure of 1-horse power. The machine exhibited by Mr. 

 Ladd at the Eoyal Society was altogether rudely constructed, and 

 was only intended to illustrate the principle ; but with this small 

 machine three inches of platinum wire *01, could be made incan- 

 descent. There is no doubt that tins principle is both ingenious 

 and valuable, and Mr. Ladd deserves great credit for the enterprise 

 he has shown in making the machine. But we cannot help asking 

 why does he not in his published papers mention his assistant by 

 name, and so give him the credit which he justly deserves for 

 having made the original suggestion, instead of merely saying that 

 it was " suggested by his assistant." Manufacturers are getting 

 too much into the habit of considering that the credit of merely 

 suggesting improvements is of trifling value in comparison with 

 that of practically carrying them out. 



A discussion on the theory of Mr. Grove's gas battery has lately 

 been going on in the French Academy. Mr. Grove supposed that 

 it was indispensable for each of the electrodes of platinum of his 

 gas-couple to be simultaneously in contact with one of the gases, 

 and with the liquid placed underneath. M. Gougoin, agreeing 

 with M. Schonbein, states on the contrary that the action of the 

 platinum does not take place except on the gases already below, 

 and that the gas-receivers should only be considered as reservoirs 

 to maintain the solutions they cover in a state of saturation. The 

 electro-motive force of the gas-couple varies curiously with the 

 state of the platinum wire. Its action is increased, as M. Matteucci 

 remarked, by heating the elements in the flame of a spirit-lamp 

 some instants before emplo} r ing it. In the most favourable con- 

 ditions, the electro-motive force of the gas-couple, constructed with 

 platinum wires not platinized, scarcely exceeds 155, taking as 

 unity the electro-motive force of a thermo-electric couple of bis- 

 muth and copper, the two solderings of which are maintained at 

 the temperatures of 0° and 100° C. The electro-motive force of the 

 couple of Daniell is represented by 193, and that of the couple of 

 Volta by 178, at the moment of being set to work. 



M. Jules Kegnauld has examined the modification which 

 mercury causes in the electric position of thallium. Experiments 

 gave the following results. There is elevation of temperature, and 

 thus a disengagement of heat, during the formation of the amalgam 



