230 Royal Society: — Mr. F. Glalton on verifying 



possible ; this is shown by dotted lines in the drawing. A cock 

 at the lower end of the coil permits of the stoppage of the circula- 

 tion of the water through the pipe. 



(4) The Thermometer Frame. 



The thermometers to be compared are huug side by side round 

 the circumference of two brass rings, IO5 in. in diameter, that are 

 attached to the side rods of a cylindrical frame. The thermome- 

 ters are held in their places against the ring by spring clips, one 

 of which is shown full size in fig. 4, and one of the rings is shown in 

 fig. 3 ; the latter slide up and down the brass rods that form the 

 sides of the cylindrical framework, and are clamped at such a 

 distance apart as may best suit the thermometer under examina- 

 tion. 



Forty thermometers can be suspended at a time. The bottom 

 of the frame is provided with six rollers — three placed radially, for 

 the purpose of guiding it up and down the interior of the water- 

 vessel ; and three tangentially and projecting below the base, in 

 order to support the frame whilst putting on or taking off the 

 thermometers. This operation is performed when the frame is 

 standing on the closed hd of the box, a circular brass ring being 

 screwed to the lid to prevent the frame running off when being 

 turned round by the operator. 



The top of the frame consists of spokes radiating from a 

 hollow socket that drops over the end of an upright steel rod, 

 which, passing through the axis of the agitator, projects above it 

 (see fig. 2). A plug is then screwed into the top of this rod and 

 clamps the frame, which is supported by it ; the frame, with the 

 thermometers, can then be rotated in the \^ ater by turning this rod. 

 This turning is effected from the outside through a wheel fixed to 

 its projecting lower extremity, into which an endless screw, 

 driven by a crank in front of the apparatus, is geared. The 

 observer, facing the glazed slit, can bring the thermometers hung 

 round the frame before him one by one as quickly as he likes. 



For the convenience of moving the thermometer frame into and 

 out of the water-vessel, a cord is carried over the apparatus round 

 pulleys, as seen in fig. 1, so that the attendant can hook its end 

 to the ring at the top of the frame, and twist or lower it with the 

 grestest facility. 



The general character of the process of comparison is to turn 

 down the gas and to close circulation in the pipe by turning the 

 stopcock; the water is then agitated, and is afterwards left at 

 rest until the set is finished. The thermometer frame is turned 

 once round forwards and once backwards in each process of com- 

 parison, each instrument being read off twice, the mean of the two 

 being the result aimed at. 



Mr. Whipple, the Superintendent of the Observatory, has made 

 at m}'- request a large number of experiments on the variations of 

 temperature under different conditions, and on other matters rela- 

 ting to the working of the apparatus. It \\illbe sufficient if I give 

 a few summarv tables of the results. 



