Laboratory at St. John's College, Oxford. 223 



both above and below in the tool-holder; so that it can be placed 

 either as shown or the other way up. Where large work is to 

 be done on a lathe of moderate dimensions this will be found 

 invaluable. 



Since June the lathe has been used, chiefly in conjunction 

 with the engine, in cutting change-wheels for Donkin's har- 

 monograpb, the set sold with the machine being quite insuf- 

 ficient for the production of the curves required for discus- 

 sions having some relation to my first results. 



Pneumatic Bellows. — The bellows has been constructed on 

 a somewhat larger scale than that originally contemplated. 

 Every increase in the size of bellows is known to conduce to 

 the steadiness of the wind. This bellows is about 6 feet long 

 and 3 feet broad. It occupies the lower portion of a frame, 

 the upper part of which carries a wind-chest supplied by wind- 

 trunks of great capacity, and a large and solid table to place 

 apparatus upon. Thirty slides altogether are provided, with 

 apertures of various diameters, from nearly two inches to 

 small fractions of an inch. The bellows itself consists of a 

 reservoir formed with direct and inverted rib, with connecting 

 guides, in the ordinary English style. This is supplied by 

 three feeders, driven by three cranks set at angles of 120° on 

 a shaft which runs the whole length of the instrument. The 

 shaft carries a handle at one end, and a pair of fast and loose 

 pulleys of large size at the other, by means of which the bel- 

 lows can be driven from the shafting or disconnected at plea- 

 sure. The bellows was required to be able to deliver wind at 

 a pressure of two feet of water. This is a very unusual test 

 for organ-bellows ; and it has not proved convenient to put 

 sufficient weight on so large a bellows ; but the bellows has 

 worked for some time at a pressure of about 1 foot of water, 

 which is amply sufficient for any thing likely to be required. 

 The pressure of ordinary organ-wind is about 2J inches; and it 

 will probably be convenient to work this bellows at from 3 

 to 4 inches for most purposes. 



When the bellows is blown by the steam-engine, a lever is 

 carried from the top of the reservoir to the regulating-handle 

 of the engine. When things are properly adjusted, a wind of 

 the most perfect evenness is obtained. It is, however, not 

 practicable to leave the entire control of the steam to the bel- 

 lows; in that case the combination would be overgoverned 

 and oscillations would ensue. It is best to regulate the steam 

 pretty exactly at the cock on the steam-pipe; and then the 

 handle of the engine itself, which is attached to the regulating 

 lever, has not too great an influence. 



With reference to the employment of wind for the evalua- 



