222 Intelligence and Miscellaneous Articles. 



" The useful work for the main current at night would most conve- 

 niently take the shape of an electric light to illuminate very efficiently 

 the Signal-office. The electric light would produce at least 50 times 

 less heat than if the same quantity of light were obtained by com- 

 bustion ; and this is no doubt a great advantage in a hot climate 

 like that of India. During the day-time the main current might 

 be used for pulling the punkhas, lifting messages, or, more generally, 

 for working a pneumatic system of despatching messages between 

 the head telegraph-office and local centres in Calcutta. If Calcutta 

 had the good fortune to possess a colder climate, it might be sug- 

 gested to use the heat developed by the main current in a coil of 

 iron wire for warming rooms. It would then only be necessary to 

 lead the wire along the walls in a manner similar to that in which 

 rooms are often heated by hot- water pipes ; only the electrical 

 method would be far more economical. The quantity of heat given 

 out by such a wire is by no means small. In one case it was equal 

 to 20473 Q, ergs per second, equal to 488 grm. degree-centigrade 

 per second. This is about equal to the heat produced by an ordinary 

 Grerman stove consuming 6 lbs. of coals per hour, supposing that 

 the loss of heat when coals burn under a steam-boiler is about four 

 times greater than when they burn in a Grerman stove. It appears 

 therefore that the heat emanating from the wire should suffice to 

 keep a moderate-sized and ordinarily ventilated room at a comfort- 

 able temperature even when situated in the highest latitude." — 

 Proceedings , Asiatic Society of Bengal, for November 1880. 



DETERMINATION OF THE COLOURS CORRESPONDING TO THE FUN- 

 DAMENTAL SENSATIONS BY MEANS OF ROTATING DISKS. BY 

 M. A. ROSENSTIEHL. 



As Maxwell has shown*, rotating disks permit us to determine 

 with great precision the laws of colour-vision. I am going to fur- 

 nish fresh proofs of that fact by showing how with their aid one 

 can find exactly the position occupied in the chromatic circle by the 

 three colours which, according to the theory of Young, correspond 

 to the fundamental sensations. 



I have taken as starting-point a chromatic circle executed on 

 sheets of paper with covering colouring-matters. The whole forms 

 a continuous succession of seventy-two colours, in which the red, 

 the yellow, the blue are at equal distances from one another, and 

 the intervals are filled by colours also as equidistant as possible to 

 the eye, with the same height of tone, and all equally clear. 



Each colour can be regarded as resulting from the mixture of 

 two others (I mean the mixture of the sensations). I proposed to 

 myself to measure the two components of each of them. 



Example. — Let us suppose that orange is a mixture of red and 

 yellow. I compose a disk of two concentric circles. The smallest 

 is formed by two sectors — one orange, the other blue ; the largest 

 comprises a red sector, a white sector, and a void representing the 

 absence of light. I set it in rapid rotation. The two circles have 

 an identical appearance if the angles of the different sectors are 

 * Trans. Roy. Soe. Edinb. vol, xxi. pp. 275-298. 



