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 to 

 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 would not fail to be an acceptable present." So 

 far Mr. Watson. In April following, was read a letter from 

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

 gives a draft of his pump ; 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 would order some- 

 body to call for it. 



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

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

 the new air-pump from England. 



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

 Your obliged humble servant, 



B.FRANKLIN. 



13 Philadelphia, Aug. 31, 1755. 



Dear 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 

 men, and all our credit with the indians ; and I fear these 

 losses may soon be productive of more, and greater. 



