M. E. Stohrer on an Improved Induction Apparatus. 57 



for other pui-poses. I shall take the liberty of describing it more 

 accurately at a future time, and to explain it by drawings, as it 

 is deserving of strong recommendation. 



One of the phrenomena in rarefied air which I had not hitherto 

 observed, and which I have nowhere found mentioned, is the fol- 

 lowing. It is known that by diifei-eut means a stratification of 

 the passing light may be obtained ; this occurs most readily in 

 the vapour of oil of turpentine or phosphorus, which, howevei*, 

 must be present in very small quantity. Whenever I obtained 

 these layers, which appeared sharply defined, I observed a motion 

 of them from one pole to the other. It is remarkable that the 

 direction of this motion was immediately reversed when the two 

 Avires were changed so as to change the polarity of the two spheres. 

 The progressive motion of the layers always takes place from the 

 positive to the negative pole. 



Although during the observation of these luminous layers, 

 which, it may be remarked, are often so sharply defined that the 

 intervening spaces are completely dark, an optical illusion may 

 easily be thought of, possibly connected in some way with the 

 play of the circuit breaker, I must mention that neither the mag- 

 nitude of the dark spaces, nor the velocity of the motion was 

 changed, when the breaker was permitted to vibrate at a difi"er- 

 ent rate. If such layers once occur, the circuit may even be 

 caused to open and close at pleasure by the hand ; the same layers 

 and the same progression of the strata will always be observed. 



I now pass to the description of a new induction instrument, 

 in the construction of which I have availed myself of my own 

 experience and that of others, in order to produce the greatest 

 possible effect. 



The apparatus (fig. 1) consists of the following principal 

 parts : — 1, the primary coil with a bundle of iron wires; 2, the 

 three siufjle induction coils; 3, the interrvptor ; 4, the discharger ; 

 5, the condenser. 



1. The primart/ coil itself is not to be seen in the figure, but 

 the u])per end of the bundle of iron wires is seen at A. The latter 

 consists of wires of 1 millim. in diameter, which stand loosely in a 

 thin cylinder of wood, so that they may be taken out of it singly, 

 '['he little bars are varnished with shell-lac. The primary coil is 

 wound on the wooden cylinder j its wire is 1 millim. thick, and 

 is formed of six layers of the double wire. The ends of the spiral 

 are connected with the clamp screws B B. The height of the 

 whole spiral is 20 millims. ; it has an external diameter of 50 

 miilims., in which a coat of strong gutta-percha, 1 millim. thick, 

 is reckoned. The wires are varnished for the sake of security. 



2. The induction spiral consists of tliree single coils, which 

 may be easily taken oiF the primary, and united at pleasure one 



