DR. PRINCE S AIR-PUMP. 



235 



I- 



IV. 



ExtraSi of a Letter from Dr. Prince, refpeSiiag his 

 Air-Fwnp. 



T is iinnecefTary here to enter into the merits of Dr. Prince's Dr- Prince's 

 air-pump, as they were noticed in the Ift. Vol. of the Phiio- ^'''-P"'"P ™f- 

 fophical Journal, 4to. edit. p. 130. The purpofe of his letter the Encyclo- 

 is to defend himfelf againft the mifreprefentations of the writer P^^^'^Britannica. 

 of the article pneumatics, in the Encyclopedia Britannica; 

 which he has done in the fupplement to the edition of that 

 work reprinting in America, where it may be prefumed it 

 will meet the eye of but few EngliPn readers. 



The Encyclopedia fays, "great inconveniences were ex- Charged with 



parienced fram the ofciiiations of the mercury in the gau^e. '"<^""v^"'eHce 



' ^ _ ... rromokulations 



As foon as the pifton c(jmes into the ciftern, the air frqm the of the mercury 



receiver immediately rufnes into the barrel, and the mercury '" '^'^^sauge. 



ftioots up in the gauge, and gets into a ftate, of ofcillation. 



The fubfequent rife of the piflon will frequently keep time 



with the fecond ofcillation, and increafe it. The defcent of 



the piflon produces a downward ofcillation, by allowing the 



air below it to collapfe ; and by Improperly timing the ftrokes, 



this ofcillation becomes fo great, as to make the mercury enter 



the pump." 



This, Dr. Prince obferves, is a very lingular account of Thlscontradift- 

 the working of the American air-pump. Itfeema to be found- ^ y * ^* 

 ed on experiment, yet it is contradided by numerous experi- 

 ments performed with the original pump, and with one on 

 the feme conftrudion, made by the late Mr. G, Adams in 

 London. Many fcientific and refpe6lable, perfoas were 

 witnefles, that no fuch extraofcillations were produced by it ; 

 but that the mercury rofe in the gauge in the fame manner as 

 it did in a double-barrelled pump of the common conftruction 

 made by Nairne., Add to this, Mr. Adams, who made the 

 firft pump in England on this plan, mentions no furh efTea, 

 either in his letter to the inventor, or in his public account of 

 it; nor does Mr. Jones, who has fi nee made pumps on this 

 plan, and given an account of their exhaufting power, wi-i-h 

 he fays, in a letter to Dr. Prince, is fully equal 'to that of 



Cuthbertfon's. 



To 



