272 PHILOSOPHICAL TRANSACTIONS. [aNNO 1777. 



smaller chimney would be sufficient to carry ofF the steam, unless the vessel is 

 much larger than what we used; yet the adhesion which is apt to take place be- 

 tween it and the tin plate when wet, might perhaps bear too great a proportion 

 to the power which the included steam has to lift it off, if it was made much 

 less. It is convenient that the chimney be not less than 2 or 3 inches long, as 

 thus the observer will be less incommoded by the steam; but it would be improper 

 to make it much longer, for the longer the chimney is, the greater disposition 

 has the air to enter into the pot between it and the cover. 



It is most convenient not to make the cover fit on tight, but to take on and 

 off easily ; and to wrap some spun cotton round that part of the cover which 

 enters into the pot, in order to make it shut closer; or, what seems to answer 

 rather better, a ring of woollen cloth may be placed under the cover, so as to 

 lie between the top of the pot and it. These methods of making the cover shut 

 close can be used more conveniently when the cover is made to enter within the 

 pot, as in the figure, than when it goes on on the outside. 



There are various easy ways by which the hole in the cover, through which the 

 tube of the thermometer is passed, may be stopped up, and by which the ther- 

 mometer may be suspended at the proper height. The hole in the cover may 

 be stopped up by a cork, which must first have a hole bored through it, large 

 enough to receive the tube, and be then cut into two, parallel to the length of 

 the hole. Another method, more convenient in use, but not so easily made, is 

 represented in fig. 1 6, which exhibits a perspective view of the apparatus ; Aa is 

 the cover ; h the hole through which the thermometer is passed ; Bb a flat piece 

 of brass fixed on the cover ; and DdEe a sliding piece of brass, made so as either 

 to cover the hole h, or to leave it uncovered as in the figure, and to be tightened 

 in either position by the screw s sliding in the slit Mm ; a semi-circular notch 

 being made in the edge Bb, and also in the edge nd, to inclose the tube of the 

 thermometer : pieces of woollen cloth should also be fastened to the edges Bb 

 and nd, and also to the bottom of the sliding piece odEe, unless that piece and 

 the cover are made sufficiently flat, to prevent the escape of the steam. In 

 order to keep the thermometer suspended at the proper height, a clip may be 

 used like that represented in fig. 17, which by the screw s must be made to 

 embrace the tube tightly, and may rest on the cover. That part of the clip 

 which is intended to bear against the tube, had best be lined with woollen cloth, 

 which will make it stick tighter to the tube, and with less danger of breaking it. 

 Another method, which is rather more convenient, when the top of the tube of 

 the thermometer is bent into a right angle, in the manner frequently practised at 

 present for the sake of more conveniently fixing it to the scale, is represented in 

 the same figure ) 6 ; cgpf is a plate of brass, standing perpendicularly on the 

 cover, and lInu a piece of brass, bent at bottom into the form of a loop, with a 



