50 CLASSICS OF MODERN SCIENCE 

 from one leg into the other by the sides of the mercury (we took, 

 I say, care), that the air at last included in the shorter cylinder should 

 be the same laxity with the rest of the air about it. This done, we 

 began to pour quicksilver into the longer leg of the syphon, which, 

 by its weight pressing up that in the shorter leg, did by degrees 

 straighten the included air; and continuing this pouring in of quick- 

 silver till the air in the shorter leg was by condensation reduced to 

 take up but half the space it possessed (I say possessed, not filled) 

 before, we cast our eyes upon the longer leg of the glass, upon which 

 we likewise pasted a slip of paper carefully divided into inches and 

 parts, and we observed, not without delight and satisfaction, that the 

 quicksilver in that longer part of the tube was 29 inches higher than 

 the other. Now that this observation does both very well agree with 

 and confirm our hypothesis, will be easily discerned by him that takes 

 notice what we teach : and Monsieur Pascal and our English friend's 

 [Mr. Townley's] experiments prove, that the greater the weight is that 

 leans upon the air, the more forcible is its endeavor of dilation, and 

 consequently its power of resistance (as other springs are stronger 

 when bent by greater weights). For this being considered, it will 

 appear to agree rarely well with the hypothesis, that as according 

 to it the air in that degree of density, and correspondent measure 

 of resistance, to which the weight of the incumbent atmosphere had 

 brought it, was unable to counterbalance and resist the pressure of a 

 mercurial cylinder of about 29 inches, as we are taught by the Tor- 

 ricellian experiment ; so here the same air being brought to a degree 

 of density about twice as great as that it had before, obtains a spring 

 twice as strong as formerly. As may appear by its being able to 

 sustain or resist a cylinder of 29 inches in the longer tube, together 

 with the weight of the atmospherical cylinder that leaned upon those 

 29 inches of mercury; and, as we just now inferred from the Tor- 

 ricellian experiment, was equivalent to them. 



(The tube broke at this point and, unable to proceed after several 

 similar efforts, Boyle tried the converse experiment — to determine 

 the springs of rarefied air. A tube, about 6 feet in length, and sealed 

 at one end, was nearly filled with mercury, and into it was placed) — 



A slender glass pipe of about the bigness of a swan's quill, and 

 open at both ends ; all along of which was pasted a narrow list of pa^ 

 per, divided into inches and half -quarters. This slender pipe be- 



