1^2 EXHAUSTING MACHINE BY MERCURY. 



of the machine, which I concieve well adapted to answer the 



end proposed." 

 Plausible In With all deference to Dr. Traill, I must suppose his 



theory. ideas are theoretical ; and they certainly appear, to those 



who have not tried such experiment, admirably calculated 



to produce a perfect vacuum on the Torricellian principle: 

 The larger the but I am inclined to think, that the larger an apparatus of 

 »P1 ara'us pro- ^^- ^j j • ^y^^ more imperfect it must be ; since every ex- 

 bably the less , ' . ,, , . " • • 



perfect the va- perienced artist well knows what extreme care is requisite 



cuum. jjj lYiakin^ barometers of the best construction, where we 



are obliged to boil the mercury to exclude air and vapour ; 

 and as the same means cannot be applied to the instrument 

 alluded to, it follows in consequence, that the air cannot be 

 completely excluded, by the simple manipulation of fillings 

 with mercury, and permitting its descent. 



Defect ill the After Dr. Traill has described tke instrument, he directs 

 the whole to be filled with mercury, and its cover then to 

 be placed on. Nov/ I believe it is well known from the laws 

 of repulsion, that it will be impossible to fill the receiver in 

 such a manner, as to admit the cover to be put into its pro- 

 per place, and at the same time exclude all the air neces- 

 sary for a perfect exhaustion, or vacuum. The state of this 



No gauge. vacuum too cannot be determined, without a gauge, for 

 which there is no provision in the instrument described. 



An apparatus, As, I have intruded thus far, I beg to say, that, in the 



^?^i'^/ *** ^'' early part of this year, I made a similar apparatus for J. G. 

 Children, Esq. F. R. S. as contrived by himself; and as it 

 appears to have a decided advantage over that of Dr. Traill, 

 I trust a brief description of it may be admitted. 



Description of It may be sufficient to say, every part is similar in prin- 



Sef' '* '^** ^'P^^ ^° ^'■- Traill's, but the recipient of small capacity, and 

 the cover marked B admirably constructed to remove every 

 objection as to the complete filling with mercury. Let fig. 

 A therefore represent the recipient ; B the cap, the under 

 side conical as shown ; C, a cock with a funnel ; D, another 

 cock on the opposite side of the cap. Now after the receiver 

 was filled as high as convenient, the cap (or stopper) was 

 put into the neck. Mercury was then poured into C through 

 the funnel, until it passed out at D (according to the law 

 of fluids finding its level), when both the cocks being turned, 



comuQunication 



