626 PROCEEDINGS OF THE AMERICAN ACADEMY. 



very low pressures by measuring viscosity. As in Maxweirs formula 

 for the oscillating disk, account is taken of the friction on and in the 

 fibre, and ou the mirror, the sphere has been replaced by a glass disk 

 oscillating- between two fixed glass disks. The whole is enclosed in a 

 glass vessel which is in connection with a McLeod Gauge and a mercury 

 pump. 



I desire to express my gratitude to Professor Trowbridge for placing 

 at my disposal everything necessary for carrying on the work, and to 

 him and to the other professors of the department for helpful suggestions 

 during the course of the investigation. 



