On the Pneumatic Paradox. 



145 



tions of recent date, I was led, without further inquiry, to describe 

 as new, several results, which, as I have since learned, had been 

 previously discovered. Mr. Hopkins, and, previously to him, 

 Mons. Clement-Desormes, in a memoir presented to the French 

 Academy of Sciences, have anticipated me in proving the exis- 

 tence of a partial vacuum between the disks. An account of 

 some experiments by Dr. Faraday, for a knowledge of which I 

 am indebted to Prof Henry, is contained in the third volume of 

 the (Quarterly Journal of Science, and among them are two or 

 three similar to some of the less important ones described by me. 

 Thus far I feel called upon to disclaim any pretensions to priority 

 of discovery. 



All of these gentlemen, if I understand them aright, attribute 

 the adhesion of the disks solely to what I have called the pri- 

 mary rarefaction, produced by the lateral expansion of the radi- 

 ating currents, in consequence of their " passing from a smaller to 

 a larger space." From their failure to discover what I have 

 termed the secondary rarefaction, the theory adopted by them 

 seems to me essentially defective. It affords no explanation of 

 the fact that, as the experiment is usually performed, the air is rare- 

 fied inward to the very orifice of 

 the tube, where no expansion of 

 the radiating currents can have 

 taken place, and, in certain cir- 

 cumstances, four inches and a 

 half into the tube itself The 

 latter singular result was obtain- 

 ed in the following manner. 



To the perforated center of a 

 plate of tinned sheet iron was 

 soldered, as represented in the 

 accompanying figure, a tube 

 eight inches long, and a quarter 

 of an inch in diameter. Holes 

 were made at intervals in it, 

 and to them were soldered small 

 leaden tubes, a few inches long, 

 to which a glass tube, bent in 



the form of a double syphon, 



could readily be adapted. Only 



fr^ 



^^ 



Vol. XL, No. 1.— Oct.-Dec. 1840. 



19 



