444 SCIENTIFIC EXPEEIMENTAL APPAEATUS. 



mg. These are by Schickert, of Dresden. One heavy balance weigh- 

 ing to about 25 kilos, and accurate to about 0.1 grm., by Schneider. 



Standard glass kilogramme on Jolly's plan, and com^jared with Ber- 

 lin standard. From Berberich, in Munich. 



The first balance mentioned is mounted on top of a case, so that 

 globes for weighing gases can be suspended beneath it. 



G5. GlocJc-worlc with Foiicault's regulator for running small apparatus 

 at a regular velocity. 



G6. Petroleum engine of three-horse power. It is capable of giving a 

 large amount of compressed air at more than 100 pounds to the square 

 inch pressure, and might be used for repeating Thomson's and Joule's 

 experiments or any others on the flow of gases. 



67. Tico splierometers] large by Meyerstein, and small by Salleron. 



QS. Several extra micrometer eye-pieces. 



G9. Apparatus for researches on the fioic of liquids. — Greatest available 

 head about 1.4 metres. 



Biological Laboratory. 



(In charge of Professor H. N. Martin.) 

 Apparatus for exact measurements. 



1. Pendulum myographion,, modified from Fisk's; available for the 

 measurement and analysis of rapid movements. The instrument con- 

 sists essentially of a ijendulum carrying a glass plate at the bottom, 

 swinging on friction rollers, and corrected for the latitude of Baltimore, 

 so as to swing in one second. Behind the pendulum is a divided arc, 

 and the amplitude of the swing can be varied from a few inches to four 

 feet. In use an electro-magnet is moved along the divided circle, and 

 then — the current being closed through it — the pendulum, on being 

 raised, is held by it. On the other side is a catch, also movable along 

 the arc. By turning a key at the side the current in the electro-magnet 

 is broken, and the ijendulum swings across and is held by the catch on 

 the other side. During its transit the movement to be analyzed is in- 

 scribed on the glass x>late, which is previously smoked. Designed by 

 A. G. Dewsmith, esq.. Trinity College, Cambridge, England. Made by 

 Elliott, London. 



2. A set of three pairs of Kouig's recording tuning forks for measur- 

 ing small periods of time ; giving respectively 50, 100, and 200 double 

 vibrations per second. 



3. Bernstein's differential rheotome, with Helmholtz's electromotor to 

 drive it. Zimmermann, Heidelberg. 



4. Two Sir William Thomson's reflecting galvanometers ; one large 

 and the other small resistance. Elliott, London. 



5. Ludivig'^s hymographion ; to give uniform horizontal movement to 

 an endless sheet of paper, on which vertical movements can be recorded 

 and subsequently measured and analyzed. The instrument is provided 



