146 



Intelligence and Miscellaneous Articles. 



struction of those which I have been employed to make, wherever this 

 could be done without impairing the accuracy of their performance. 



One of my first efforts was directed to that most valuable instru- 

 ment the air-pump, which 1 shall endeavour to show I have improved 

 so veiy materially, as to be able to furnish one capable of effecting as 

 complete an exhaustion as the most perfect form of the instrument 

 hitherto devised, and, at the same time, nearly as simple and as cheap 

 as its most imperfect form. I mentioned my views on the subject to 

 several gentlemen qualified to judge of their correctness, and soon had 

 an opportunity of putting them to the test of experiment. I received 

 an order to make one for Mr. Lees, lecturer on mechanical philosophy 

 in the School of Arts here, on condition that he was to be permitted 

 to return it, if, on trial, it was not found capable of executing all 

 that I had led him to expect. This pump, through the kindness of 

 Mr. Lees, in whose possession it has been for the last eighteen months, 

 was exhibited to the Society for the Improvement of the Useful Arts, 

 on the 19th of December 1827 *. 



Believing the only useful part of Cuthbertson's improvement of the 

 air-pump to be the contrivance for opening the valves at the bottoms 

 of the barrels, mechanically, I was of opinion a pump would perform 

 nearly, or altogether as well, divested of all the other peculiarities of 

 his instrument, and possessing the decided advantages of being cheaper 

 and much more easily kept in order. 



The Figure is a section of one of the 

 barrels of my pump, in which I employ 

 metallic valves v v' at the bottom of the 

 barrels, and waxed silk ones S S' in the 

 pistons, laying aside Cuthbertson's me- 

 tallic valves in the pistons, removing all 

 his apparatus from the top of the barrels, 

 and leaving the pistons exposed to the 

 atmosphere^ as 1 consider all those con- 

 trivances to be unnecessary, although 

 it has been uniformly held essential to 

 a good air-pump, since the time of 

 Smeaton's invention, that the pressure 

 of the atmosphere should be taken off 

 the piston-valves ; and my reason for 

 doing so is, that the air will be always 

 so compressed in the barrels, by the descent of the pistons, as of itself 

 to have sufficient elastic force to open the silk valves in the pistons, 

 the capacity of the barrels being each several thousand times greater 

 than the space between the two valves, when the piston is at the 

 bottom. In fact, by making the under side of the piston and the 

 bottom of the barrel fit each other, which, with the assistance of the 



* The instrument had been previously submitted to the examination of 

 Dr. Turner, one of the Secretaries of the Society of Arts, who reported that 

 he had minutely examined it, and was perfectly satisfied with its performance. 

 On his representation to the Council of the London University, I have since 

 received an order to make one for the chemical class of that Institution. 



oil 



