VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 413 



Thermometers described. — a represents a mercurial thermometer, with an air-bulb at the top, 

 graduated 628 degrees below the cypher, and marked at every second degree. Makers, Nairne and 

 Blount ; the scale box-wood. 



b, another mercurial thermometer graduated to 526° below the cypher, each line representing 2°, 

 made by Nairne and Blount ; the scale box-wood. 



c, is a fine mercurial thermometer, with an air-bulb at the top graduated 2300° below the cypher, 

 each division containing 5° ; the scale made of box, by Troughton. 



d, a small spirit thermometer on a box scale, made by Troughton, and divided to every single de- 

 gree down to 1 60° below the cypher, 



e, Another spirit thermometer, by the same maker (Troughton) graduated 90° below the cypher ; 

 the scale box. 



f, a small mercurial thermometer, on an ivory scale, divided at every 5° between 220° above and 

 250° below the cypher ; made by Nairne and Blount. 



G, another mercurial thermometer, every way like the last-mentioned, except only reaching from 

 215° above to 250° below the cypher ; by Nairne and Blount. 



H, a spirit thermometer, made by Nairne and Blount, with which Mr. H. made meteorological 

 observations from the year 1774. 



Mr. H. next gives a register of the height of all these thermometers, as ob- 

 served several times every day, in the natural cold, from Nov. 23, 1781, till 

 March Q, 1782; during which trial the thermometer a was uniformly the 

 lowest, and the greatest degree of cold indicated by it was — 82°, or 82 below 

 0, which was on Feb. 22, at 7 in the morning. He then records an experiment, 

 made Dec. 15, 1781, with an artificial mixture, in which the lowest state of the 

 thermometer was — 448-i-, or 448-L below O. And on which experiment he re- 

 marks as follows : viz. That, finding the thermometer on the evening of Dec. 

 14, was 18° below the cypher, he concluded the morning would afford an oppor- 

 tunity to make an attempt to fix the point at which quicksilver begins to freeze ; 

 he therefore put a bottle of spirit, nitri fortis on the top of the house in open 

 air, that it might be of the same temperature when it was to be used. At 7 in 

 the morning of the 15th, the thermometers were about 23° below O ; he there- 

 fore made preparations for the experiments, getting the quicksilver out into the 

 air, providing glass tumblers for mixing the nitrous acid with the snow, &c. 

 He put as much quicksilver into a glass cylinder as, when the thermometer p 

 was introduced, just filled the bulbous part of the cylinder ; the scale of the 

 thermometer did not reach the length of the tube by about 3 inches. The ex- 

 periment was made in the open air, on the top of the Fort, with only a few 

 deer-skins sewed together, placed to windward for a shelter : there was plenty of 

 snow, 18 inches deep, on the works, and the thermometers were close at hand. 

 In thrusting the thermometer f into the quicksilver, the instrument rose to the 

 cypher, but soon began to descend again ; but being unwilling to lose time, Mr. 

 H. stuck the apparatus into the snow, the sooner to bring it to the temperature 

 of the air. He was in hopes, by shifting the instruments into 3 fresh mixtures, 

 he should have been able to have produced a greater degree of cold than by one 



