27 



tripod, and a graduated tube below. The mass having been 

 weighed in air, it is placed in the jar with the water up to a 

 certain level ; by the insertion of the mass the level of the 

 water is raised, and the quantity that must be let out to bring it 

 to its former level can be passed through the stop-cock into the 

 graduated tube. Hence the bulk, and therefrom the weight of 

 water displaced, is determined. 



81. Nicholson's areometer. Constructed to carry 

 1*17 grammes. 



E. 52. 1889. 



Consists of a large glass cylinder, with floating areometer. 

 This is now supported on a wooden disc, but .in use the cylinder 

 is filled with water, and the areometer is placed in it. The latter 

 is composed of a scale pan at the top, with brass cylinder below, 

 and about 1 inch below that a hollow cone. This serves first to 

 determine the weight of water displaced by any moderate sized 

 substance which, when placed in the upper scale pan, depresses 

 the cylinder to a given position, but when placed in the lower 

 scale, does not depress it so much, and weights have to be added 

 to the top scale pan, to counterbalance the water displaced. The 

 weight in air may be determined by the same apparatus by 

 observing the depression caused by placing the substance in 

 the upper scale pan, and producing an equal depression by 

 weights placed there instead. 



82. Nicholson's areometer, improved form. 

 E. 54. 1889. 



This is very similar to No. 81, but a perforated plate movable 

 about a horizontal axis takes the place of the hollow cone for 

 supporting the substance when being weighed in water. 



83. Jolly's spring-balance. 



E. 51. 1889. Made by Berberich, Munich. 



This consists of an upright square hollow beam, on a tripod 

 stand, with levelling screws, with a mirror in front. In front of 

 the mirror is supported a long delicate wire spring, which is 

 movable by means of a rod sliding within the beam, and 

 clamped behind. This carries at the base two scales, one 

 below the other, and also a bright bead. Below it stands 

 a platform, which may be raised or lowered, and on which 

 is placed a tumbler full of water. The principle of action is 

 essentially the same as that of Nicholson's areometer ; i.e., the 

 weighing of the substance is performed by making it and the 

 equivalent weights have the same effect on the position of 

 the scales, only this is determined, not by their position in 

 relation to the surface of the water, but by the lengthening 

 of the springs, when the substance or weights are placed in, the 



