Vi SCIENCE—ADVERTISEMENTS 
THE BROOKS’ INDUCTOMETER 
In the Brooks’ Inductometer is offered 
a compact form of variable inductance, 
with a self inductance range of 5 to 50 milli- 
henrys, possessing the following advan- 
tages: 
1. A fair degree of astaticism, which 
tends to eliminate errors due to stray 
j field effects. 
2. It is less expensive and ast the 
same time fully as accurate as the Ayrton- 
Perry instrument. 
3. It occupies less space than the 
Aryton-Perry form. 
The instrument has a very nearly uniform scale, obtained by properly proportioning the coils. 
It may be used as a mutual inductance. 
It has a good ratio of maximum to minimum inductance (about 9 to 1) and also has as high 
a time constant as is consistent with good design and moderate size. 
The instrument is fully described in Bulletin No. 152, a copy of which will be sent upon request. 
THE LEEDS & NORTHRUP CO. 
ELECTRICAL MEASURING INSTRUMENTS 
4921 STENTON AVENUE | PHILADELPHIA 
In every laboratory where electricity is used, there is need for 
variable resistances—and to meet such requirements 
we offer a well tried series of 
“JAGABI’ SLIDING CONTACT 
TUBE RHEOSTATS 
Hundreds of them have been sold during the past three years, to various Govern- 
ment Departments, Universities, Colleges, Technical Schools, Industrial Com- 
panies, etc.—and have “made good” under every-day service conditions. 
WRITE FOR ILLUSTRATED DESCRIPTIVE BULLETIN 887 
JAMES G. BIDDLE 
1211-13 ARCH STREET, PHILADELPHIA 
