162 THE SIGNS OF LIFE 



side of the general laboratory as figured. (The extra galvanometer, 

 G 3 is a separate low-resistance instrument, for use with either table, 

 to give thermo-electric readings of temperature ; it is worked by a 

 constantan-iron junction, the varying E.M.F. of which is balanced 

 by compensation ; the compensator is graduated so that a known 

 length has a known temperature value.) 



Each pair of galvanometers, G l and G 2 , G 4 and G 5 is intended to 

 be used as described above ; for ordinary work, only the observation 

 galvanometer G 2 , or G 4 , is used ; when a phenomenon deserving to 

 be recorded presents itself, the recording galvanometer G p or G 5 , is 

 unplugged, and the recording surface is set in motion. 



The apparatus is thus utilised in the general laboratory without 

 suffering any disturbance from other work in progress in the same 

 room. 



Lippmami's Capillary Electrometer, like the galvanometer, can 

 be used (i) as a refined instrument of research for the special 

 purposes of electro-physiology, in which case its photographed 

 indications must be mathematically analysed ; or (2) as an ordinary 

 laboratory instrument for the summary inspection and the con- 

 venient demonstration of electrical changes that are too brief or 

 in too rapid succession to be readable by galvanometer e.g., the 

 electrical changes accompanying the beat of the heart. By means 

 of very simple recording apparatus, the value of the electrometer 

 as an ordinary instrument of inspection and demonstration is greatly 

 enhanced. In this laboratory a capillary electrometer is currently 

 xised in place of a demonstrating galvanometer. The image of 

 the capillary in the projection microscope, with J to ^ objective, 

 is first thrown upon a transparent screen, where the movements 

 of the column of mercury are shown. An opaque screen with a 

 narrow vertical slit, behind which a vertical photographic plate 

 travels horizontally, is then placed on the lecture-table, so as to 

 receive the image of the moving column of mercury, which is thus 

 photographed. And lastly, the developed photograph is exhibited 

 in the ordinary projection-lantern. Thus the record of move- 

 ments that have just been seen, is exhibited and examined. In 

 this manner there is no difficulty in demonstrating in the course 

 of a quarter of an hour ist, the electroscopic indications of, e.g., 

 a frog's heart ; 2nd, the photographed records of such indications. 



The diameter of the capillary column of mercury is, e.g., 25 ft. 



