132 



SCIENCE 



[Vol. IV., No. 



structed by Zachariae of Leipzig, and has been 

 described by Dr. Bowditch in his communica- 

 tion, t; Ueber die €igenthumlichkeiten der reiz- 

 barkeit, welche die muskelfasern des herzens 

 zeigen " (Ber. saclis. gesellsch. wiss. Leipzig, 

 xxiii. 1871, 658). 



Besides the more ordinary forms of inter- 

 rupter in common use, the 

 laboratory possesses several 

 home-made ones, which have 

 proved useful, and are set 

 up in the interrupter-case as 

 required. One is merely a 

 simplified Bernstein's acous- 

 tic interrupter, in which a 

 steel bar of variable length 

 (determined by a sliding 

 clamp) is kept swinging by 

 a temporary mag- 

 net above, while a 

 platinum point 

 makes and breaks 

 in a cup of mer- 

 cury below. An- 

 other very simple 

 a n d inexpensive 

 form, which is easi- 

 ly made, and prob- 

 ably admits of more 

 general applica- 

 tion, consists of a 

 steel rod swinging 

 on a knife-edge at 

 one end, while the 

 other is attached to 

 a long spiral spring 

 fixed above. The 

 swing is deter- 

 mined b}- the ten- 

 sion of the spring, 

 and the position of 

 variable weights on 

 the bar. This ar- 

 rangement has 

 proved useful for 

 slow interruptions, 

 one to three in a 

 second, the appa- 

 ratus before men- 

 tioned permitting four to ninety in the second. 

 Against the wall, above the end of the chem- 

 ical table on the southern side of the room, is 

 the respiration apparatus (RA), whose con- 

 struction is made clearer by the adjoining 

 sketch (fig. 5) . It is merely a water-bellows of 

 the ordinary form, receiving its water-supply 

 by the upper pipe at the right, from the con- 

 stant-pressure tank at the top of the building. 



Fig. 5. — Respiration apparatus. 



Lettering to respiration apparatus. — A, water-motor; BC, stop-cocks 

 for water-supply ; D, revolving stop-cock; EFGHR, stop-cocks direct- 

 ing stream of ar; /, regulating-cap; JEW, water-bellows; L, air- 

 supply from bellows ; M, pipe to lecture-room ; N, pipe to working- 

 tables ; 0, filter-pump ; P, air-pipe for blast-lamp ; Q, rubber pipe of 

 filter-pump; 1\ mercury-gauge; V, gas for ble.st-lamp; W, air-inlet 

 to bellows. 



The water enters the upper cylinder (J"), and 

 passes down through the pipes marked K, into 

 the air-chamber in the basement two stories be- 

 low, the compressed air coming up to the labo- 

 ratory by the pipe L. If the water enter the 

 bellows by the lower stop-cock (O), a steady 

 blast of air is obtained, which may work a blast- 

 lamp at P, or, by a proper clos- 

 ing of the stop-cocks, be car- 

 ried to the glass-blowing table 

 (BL) , 10.5 metres awa} T ; a gas- 

 pipe (N) being laid for this pur- 

 pose along the wall, and under 

 the edge of the long working- 

 table. By a different closure of 

 the stop-cocks, the air-stream is 

 directed to the lecture-room 

 through the pipe M, reaching 

 the table at A. Rubber hose 

 attached to a stop-cock below 

 the long wall-table permits the 

 use of the same blast of air on 

 any of the other working- tables 

 of the room. If the upper stop- 

 cock (B) be opened, and the 

 lower one (C) be closed, the 

 water passes through a small 

 motor (A) before entering the 

 bellows ; thus doing double 

 work, first in falling from the 

 tank to the motor, and then in 

 falling further to the 

 basement. The mo- 

 tor gives motion to 

 the cone below, and 

 a small stop- cock in 

 the axis at D regu- 

 larly breaks the 

 otherwise constant 

 stream of air, which, 

 opening the stop- 

 cock H, and closing 

 that at 6r, permits 

 free passage to 

 this portion of the 

 apparatus. A slot- 

 ted cap (/) regu- 

 lates the amount of 

 air delivered, while 

 the rapidity of the interruptions can be nicely 

 adjusted by the amount of water flowing through 

 the motor, and by the size of the wheel used 

 on the cone. Another combination of high 

 pressure and slow movement can be obtained 

 by so adjusting the stop- cocks B and C that 

 more or less water enters the bellows without 

 passing through the motor. The large wheel 

 and the cone are on sliding boards, so that 



