SCIENTIFIC EXPERIMENTAL APPARATUS. 435 



2. Machine for original graduation of circles from 1-incli to 15-incli 

 disk. 



3. IMachine for shaping and polishing diamonds for ma^rking on glass 

 and on all kinds of metals. 



4. Microscope comparator for short lengths. 



5. Comparator for long standards of length. 



6. In x^rocess of construction at the Woltham Watch Factory: A uni- 

 versal line graduation engine. This machine is designed : 



(1). To rule N^obert's bands. 



(2). To graduate both short and long standards of length. 



(3). To rule diffraction gratings in which — 



(a) Any required relation between the relative width of the lines and 

 the spaces may be secured. 



(b) Errors of any required magnitude may be introduced, whether in- 

 dividual or systematic, without interference with the remaining gradua- 

 tions. 



Harvard University. — Medicax School PHYSioLoaiCAL Labora- 

 tory. 



(In charge of Prof. H. P. Bowditch.) 



1. ThomsoTi's galvanometer, No. 26, Elliott Brothers. Eesistance at 

 550 F. =5,995 B. A. units. 



2. Wiedemann'^s galvanometer, with mirror and two pairs of coils of 4,000 

 and 98 turns respectively. 



3. British Association unit of resistance, No. 74, right at 15.5° C. 



4. Fendulum myograph, described by Dr. J. J. Putnam at the Ameri- 

 can Academy, March, 1879. 



5. Cylinder chronograph : Baltzar, Karolinen Strasse, 14, Leijisic. 



6. Chronograph, with long roll of paper. Baltzar. Leipsic. 



7. ClocTc for making or breaking an electrical circuit once in 1, 2, 3, 4, 

 5, 10, 15, 20, 30, or GO seconds, the duration of the make or break varia- 

 ble from to 4 seconds. 



Stevens Institute op Technology, Hoboken, N. J. 



(For the use of this apparatus application may be made to Prof. A. M. Mayer.) 



1. Apparatus for the determination of coefficients of expansion. — Con- 

 sists of the tube (invented by Professor Mayer) to hold the rod under 

 measurement. This tube is so constructed that the rod up to its termi- 

 nal planes is kept permanently at the temperature of melting ice, or at 

 the boiling-point, or at any intermediate temperature, by passing a cur- 

 rent of water or hot oil through the tube; at the same time the terminal 

 Ijlanes of the rod are exposed for abutment against micrometer screws, 

 «&c. The rod is supported in the tube at quarters of its length from its 



