158 



Prof. J. C. Bose. On the Continuity of [Apr. 18, 



Influence of Pressure. — Pressure also has pronounced effect on mole- 

 cular response. Moderate increase of pressure increases the sensi- 

 bility, but too great an increase may cause loss of sensibility. In sub- 

 stances which are nearly neutral, pressure variation may even cause 

 reversal of response. 



Again, the same receiver may, owing to some molecular modifica- 

 tion, exhibit a response opposite in sign to the normal. But subjection 

 to this continued stimulation of radiation, generally speaking, converts 

 the abnormal response into normal. Exactly parallel instances will 

 be noticed in the case of response to mechanical stimulus and to light. 



We thus see how the response is dependent on the molecular con- 

 dition, and how a change of this condition may even give rise to a 

 reversal of response, say, from a diminution to an increase of resistance. 

 The nature of the chemical substance, the molecular condition, the 

 intensity and duration of radiation, the pressure, the temperature, and 

 even the electromotive force used for detection, are the factors which 

 are instrumental in the modification of the final response. I have 

 already shown* how the increasing effect of continuous radiation may 

 produce molecular reversal. There may thus be one or more reversals. 

 It is probable that the other variables may also produce similar 

 reversals. 



3. Recording Apparatus. 



In the following investigations, the electrical effects, either the 

 conductivity or the electromotive variations, due to external disturb- 

 ances of various durations, have to be observed. It is also necessary 

 to note the time-relations of the after-recovery from these effects. The 

 conductivity and electromotive variations can be deduced from the 

 observed varying deflections of the galvanometer. When the varia- 

 tions are rapid, the observation requires great alertness and is very 

 fatiguing. This difficulty is still greatly enhanced when simultaneous 

 time-observations have to be taken. It thus becomes necessary to 

 bave at least two observers ; the process of observation is made slow 

 and tedious, and the accumulation of results by this method is very 

 tardy. But in the apparatus now to be described, the mode of pro- 

 cedure has been very much simplified, affording facilities for quick and 

 highly accurate observations. 



The apparatus is a modified railway myograph. (See fig. 1.) The 

 moving platform carries squared paper (divided into i ncn ) on 

 which the record is made. The platform moves uniformly by clock- 

 work, and the rate of travel of the paper may be roughly adjusted 

 by means of different-sized pulleys, or more finely by the clockwork 

 governor. The usual rate is 1 inch in 30 seconds, and one small 

 division of the paper measured horizontally is thus equal to 3 seconds. 



* Loe. cit. 



