300 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



pierced with a circular aperture in the centre, that in the upper surface 

 being open, and that in the lower closed by a plate of glass. On the top is 

 screwed a plate s, with a deep annular groove to hold the thermometer- 

 bulb, the tube of which lies in a groove along the upper surface of the box 

 to the left. A lamp L is placed under the mica cylinder, and thereby warm 



Fig. -19. 



air is made to pass through the box, the heat being transmitted from the 

 centre plate into the object laid upon it. It is isolated from the stage T by 

 means of an ebonite ring h. 



Dr. Beale also in 1865 * described and figured a simple plan (fig. 50) 

 of heating objects by hot air. It consists of a long copper box, open at both 

 ends, the middle part of which lies flat on the stage One end is bent down 

 obliquely so as to project over the side of the stage, while the other is 

 similarly bent up. A spirit-lamp being placed at the lower end a current 



of hot air passes through the box and escapes at the upper end. The centre 

 of the box has its lower wall composed of glass, while at the upper part is 

 an opening to allow of the hot air reaching the slide. 



Valentin's stage described under (4) Water infra, can also be used as a 

 hot air stage. 



2. Electricity. — Prof. S. Strieker recommends j the use of electricity as 

 a means of heating a stage, thus describing it : — A better method than any 

 consists in the conversion of a constant current of electricity into heat. In 

 microscopical investigation only a very small absolute quantity of heat is 

 required, and indeed it is not necessary to warm the stage in its whole 

 extent, but only its centre, or what is still better, the cover-glass placed on 



* 'How to work with the Microscope,' 3rd ed., 18G5, p. 129 (1 fig.). See also 5th 

 ed., 1880, p. 189 (1 fig.). 



t Strieker, S., ' Mauual of Human and Comparative Histology.' Transl. by H. Power, 

 1870, pp. xii.-xvii. (3 figs.) 



