FROM WOOD AND CuAl,. 1 J 



curved to fit the pipe, and is of Bufficienl size to cover the 

 aperture, and rest upon the pipe The bulb of the thermo- 

 meter is suspended in the centre of the pipe, by the brass scale 

 being made shorter than usual, and resting on the tin plate. 

 wtiich is secured in its place by a small quantity of clay lute. 

 This thermometer is used to measure the temperature of the 

 air within the pipe, previous to its passing into the chimney; 

 and as I have never found the hulh discoloured by the car- 

 bonaceous particles in the smoke, and thereby rendered raor< 

 sensible, as it was feared would be the case, 1 am induced to think 

 very little ever reaches it, being previously deposited in tin 

 pipe. 



Fig. 6, is another mercurial thermometer, suspended from 

 the side wall of the room. Both these were made expressTj 

 for my experiments, and to correspond in their scales (which 

 are Fahrenheit's) with the greatest possible accuracy. The 

 thermometer, Fig. 6, is used to measure the temperature of 

 the air in the room, and is placed on a line with that in the 

 pipe, at twelve inches distance. The hulh is screened by a pint 

 of bright planished tin. to prevent the influence of heat radiated 

 from any part of the stove or pipe, while it dors not prevent 

 a free access of the air in the room, to the hulh of the thermo- 

 meter. 



Fig. 7. is Mr. Leslie's differential thermometer, on.- half of 

 which is passed through an aperture in the hoard partition into 

 the exterior room, and is secured in its place by a divided cork, 

 which encircles a part of the syphon at the bottom of tin- iii 

 strument, and closes the aperture. Both bulbs are perfectly 

 screened by large pieces of bright planished tin, not shown in 

 the. engraving. This instrument, as its name denotes, inci- 

 sures only the different of temperature in the two munis, and 



as it does this with peculiar delicacy, it is admirably adapted 



to my purpose, the accuracy of my experiments depending in 

 a great measure on the uniform difference of temperature in 

 tin two rooms : and 1 am under obligations to its inventor, and 

 also, to Dr. Hare, as it was jn consequence of tie sugjp Jtion "I 

 the latter gentleman, that tins instrument was added to my 



VOL. III. — D 



