Original Letters of Dr. Franklin. 167 



ted an air-pump, by which we are impowered to make 

 Boyle's vacuum much more perfect than heretofore. By a 

 Well conducted experiment, which admits of no doubt as td 

 Its truth, I have seen by this pump the air rarified to 1000 

 times Its natural state \ whereas, commonly, we seldom ar- 

 rive at 150. As the promotion of the mechanic arts is a 

 considerable object of our excellent institution, if this gen- 

 tleman could be prevailed upon to communicate to the Royal 

 Society that particular construction of his air-pump, which 

 enables it to execute so much more than those commonly 

 in use, it w^ould not fail to be an acceptable present." So 

 far Mr. Watson. In April following, w^as read a letter from 

 Mr. Sweaton, in which he describes his improvements, and 

 gives a draft of his pump j the whole too long to transcribe; 

 but it appears to me that the machine being rather simpli- 

 fied, than more complex, can scarce cost more than one of 

 the old sort, though the price is not mentioned. By only 

 turning a cock, it is at pleasure made a condensing engine. 

 An advantage the others have not. 



I have seen nothing of your searchers. 



Mr. Parker has received Bower, but writes me that he is 

 at a loss how^ to send it, and desires you w*ouId order some* 



body to call for it. 



I shall send the dollars for Mr* Mix- per next post. For 

 1 fancy you will not now buy this apparatus here, but chuse 

 the new air-pump from England. 



Biy respects to all friends, concludes from, dear Sir, 



i^- 



Your obliged humble servant 



B. FRANKLIN. 



r 



13 Philadelphia, Aug. 31, 1755, 



Hear Friend, 



I have been employed, almost all this summer, in the 

 service of. our unfortunate army, and other public affairs, 

 that have brought me greatly in arrear with my corres- 

 pondents. I have lost the pleasure of conversing with 

 them, and I have lost my labour: I wish these were the 

 only losses of the year : but we have lost a number of brave 

 n»en, and ail our credit with the indians ; and I fear these 

 losses may soon be productive of more, and greater. 



