22 Transactions of the Society. 



from it ; if great exactness be required steam can be replaced by a 

 current of warm water or saturated solution of chloride of calcium, 

 wliich give out only specific lieat, and that nearly equally through 

 the whole length of the tube. In either case the box is filled with 

 recently boiled distilled water or a saline solution, and placed, with 

 a non-conductor intervening, upon the stage of the Microscope, so 

 that the optic axis corresponds with the centres of the apertures ; 

 one of the forked tubes is then connected with the hot fluid, the 

 other with a supply of ice-cold water, and the exit end of the 

 copper tube with an empty vessel. The object is now placed upon 

 the thin glass stage, covered with another thin glass, and sur- 

 rounded with a cardboard shade and focussed. The heating agent 

 is circulated through the copper pipe until the required tempera- 

 ture is attained, the tap can be then turned off", and if a sudden 

 reduction of temj)erature be necessary the tap which communicates 

 with the cold water turned on. 



If a temperature above the boiling-point of water be required, 

 the box is filled with glycerine, and the heat from a spirit-lamp 

 conveyed to it by means of a projecting copper plate, one end 

 being in contact with the bottom of the box, the other in the flame 

 of the lamp. In this way any ordinary temperature can be 

 obtained, but it is not so comfiletely under control as the steam, 

 there being a rise of some 10^ after removing the source of heat. 



If a very low temperature is wanted, all the metalwork is 

 covered with felt, and the box filled with clean crystals of ice and 

 salt and water. 



This stage is specially adapted for those cases where a rising 

 or falling temperature is required. It was originally contrived 

 for studying the tumefaction of starches, noticing the temperature 

 at which the various granules burst, but I have found it useful 

 also for ascertaining roughly the melting-points of fats, by 

 observing when the crystals in them disappear; and for jellies, 

 resins, and other structureless, easily fusible, substances, by noticing 

 when small particles assume the liquid form ; and it will obviously 

 have many other applications. 



