1896.] Scientific Instruments used by the late Dr. Joule. 357 



The paper was published in the ' Philosophical Magazine,' May, 

 1845, and also in the ' Collected Papers,' pp. 171 — 189, where a full 

 description may be found, including a detailed account of anew stop- 

 cock. 



A notice of the second pump, a compressing air-pump, may be 

 found on p. 531 of the 'Collected Papers;' in this instrument the 

 cylinders, two in number, were made of great length, in order to get 

 rid of the necessity of packing, being 20 in. long and 2 in. in diameter. 

 Joule says that air can be readily compressed by the pump to 

 16 atmos. These two pumps were made under Joule's direction, and 

 with a little care would be in perfect working condition. 



The Thermometers. 



The thermometers used in Joule's determinations of the mechanical 

 equivalent of heat have already been examined by Dr. Schuster, 

 ' Phil. Mag.,' June, 1895. Several thermometers, however, of less 

 importance remain at Sale. 



Instrument for Calibrating Thermometers. 



This is a small instrument, made for Joule by Mr. Dancer. It 

 consists of a brass base with a groove for holding thermometers, over 

 this is fixed a small microscope, which may be moved forwards by 

 means of a fine screw with a graduated head ; the instrument is 

 mentioned on p. 175 of the ' Collected Papers,' vol. 1. 



Two Tangent Galvanometers. 



These galvanometers were not constructed by Joule himself, but 

 were made for him, and under his directions, by the firm Abraham 

 and Dancer, of Manchester ; one of these instruments was used for 

 measuring the electric current in the determination of the mechanical 

 equivalent of heat from the thermal effects of electrical current ; its 

 needle is suspended by a silk fibre, the torsion of which, in accurate 

 experiments, must be allowed for. I found three, coils belonging 

 to the instrument ; one of them consists of a single circle of thick 

 copper wire, the second contains about ten revolutions of finer wire, 

 and the third a large number of revolutions of still finer wire. These 

 coils are mounted on wooden rings 12 in. in diameter, which slip on 

 to the framework of the galvanometer, and may be removed or 

 changed in a few seconds. 



The smaller instrument, which is about half the size of the larger, 

 has three similar coils, 6 in. in diameter, belonging to it. 



I hoped to have been able to discover some of the MSS. of Joule's 



