186 The Rev. J. B. Reade on the Oxyhydrogen Microscope, 



thing would be easier than to direct a continued current upon 

 a thin screen of ghiss placed just behind the object in the mi- 

 croscope, by which means the uniform and low temperature 

 thus steadily maintained would ensure perfect safety even for 

 the most delicate animalcules. 



Under the impression that some change would be indicated 

 by the thermometer if a current of air were impinged upon 

 it when it indicated the ordinary atmospheric temperature, I 

 directed against the bulb about thirty blasts with the bellows. 

 I confess I was not prepared to find, after just witnessing the 

 rapid fall of the mercury, that a decidedly opposite effect woukl 

 be produced. The mercury, however, now rose in different 

 thermometers, placed both in the house and also in the open 

 air, between five and seven degrees. In each experiment the 

 bellows, before they were used, had acquired the temperature 

 of the surrounding air, and the first four or five blasts pro- 

 duced at least one third of the whole elevation. We have, 

 therefore, before us these two facts, that a current of common 

 air is a powerful absorbent of the rays that occasion heat ; and 

 that in the blast of bellows by which this current is main- 

 tained there are equal and opposite forces tending to produce 

 equilibrium. These two forces consist in a refrigerating and 

 a calorific current, which have each a separate existence. The 

 former is effective if the mercury be artificially raised, and the 

 latter if it indicate the temperature of the air. In the first 

 case the calorific principle in the solar ray is imparted to the 

 current of air and absorbed ; and in the second, the calorific 

 principle in the current of air is imparted to the thermometer 

 and retained. And hence it must be admitted, however it may 

 appear to contradict our sensations, that the blast of a pair of 

 bellows is at least 5° warmer than the air they receive. To ac- 

 count for this fact it is only necessary to refer to the general 

 law established by Clapeyron, whose memoir on the motive 

 power of heat has found a place in Part I. of Mr. Taylor's new 

 and very valuable quarterly publication entitled " Scientific 

 Memoirs." The law at which Clapeyron has arrived, and 

 which is applicable to all the substances of nature, solid, li- 

 quid *, or gaseous, is, that if the pressure supported by differ- 

 ent bodies, taken at the same temperature, be augmented by 

 a small quantity, quantities of heat will be disengaged from 

 them, which will be proportional to their dilatability by heat. 

 But it is beside my purpose to enter further into this subject. 

 I have already accomplished the object I had in view by show- 

 ing that the free passage of a current of air absorbs the calo- 



* The impact of a current of water on a thcnnometer produces an ef- 

 fect similar to the impact of a current of air. 



