ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



717 



in turn rests the metal disc, carrying the centrifugal tubes. This 

 disc is of cast steel, 14 in. in diameter, and weighing 50 lb., drilled to 

 carry twelve stout glass tubes, 6j by 1|- in. each, holding rather over 

 50 ccm. of milk. The disc, it will be noticed, is not fastened to the 

 bearing spindle, it merely has a conical cup in the centre of its under 

 surface, which receives the rubber cone that forms the head of the 

 spindle, the friction clutch being quite sufficient to transmit the speed 

 to the disc without the least diminution. This rubber head, on account 

 of the amount of play it allows, serves a very important function, in 

 that it renders the machine practically self-centering and automatic in 

 its balancing. For instance, if only two tubes full of milk are placed 

 in the machine, even in two contiguous holes, the machine can be run 

 as rapidly and as smoothly as when the disc is either empty or com- 

 pletely filled with tubes. 



The central aperture in the disc, through which the tubes are intro- 

 duced, is closed by a copper cap which screws into the body of the disc, 

 and the disc itself is enclosed in a copper basin, with a loose cover ; 

 both these details being introduced in order to lessen the air resistance 

 the machine has to overcome. 



Electric High-speed Centrifuge. — Fig. 165 represents this instru- 

 ment, constructed by Messrs. R. and J. Beck (Ltd.), which was exhibited 



at the Meeting of the Society on October 15th. It may be made to run 

 by an electric current at a very high rate of speed, regulated within 

 certain limits by the interposition of different resistances. 



