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which is here defcribed ; and from that time 'till the laft fum- 

 mer (1785) it lay by me negledled, bad health, &c. diverting 

 my attention from it ; for the whole of it, except the forging 

 the iron-work, was made by myfelf without affiftance. At 

 length, being loth to lofe my labour, I put the laft hand to it. 

 Before it was finiflied, I was acquainted with the conClrudlion of 

 Mr. Smeaton's air-pump, with its improvements, but had not 

 heard of Mr. Cuthbertfon's ; which, as well as Mr. Smeaton's, 

 I find is conceived on the fame principle with mine, yet the ap- 

 plication of that principle in the machine here defcribed, being 

 exhibited in a much more fimple conftrudlion, it will I am 

 perfuaded be found to perform better and with more certainty 

 than the former, on which perfuafion only I am induced to 

 publifh it. The reader will eafily underftand what is hereafter 

 faid of its theory, after he has confidered its conftrudlion. 



The principal parts of it are one barrel and pifton, one 

 ftop-cock, one valve, and two pipes of communication. 



N. B. The pump here defcribed is a portable one, and fo 

 contrived as to be confined in a very fmall fpace ; but it may 

 be made of a different form, and with two barrels, though not 

 conveniently. 



Fig. I. is a perfpe(5live view of the whole machine as it lies 

 before the operator. Fig. 2. is a back view of the fame. 



Vol. VI. S s The 



