SCIENCE—ADVERTISEMENTS 
The L. & N. 
High Sensitivity Galvanometer 
Aninstrument 
of extremely 
high sensitivity, 
yet one with 
which it is a 
leasure to work 
ecause it is very 
easily set up and 
its working char- 
acteristics are all 
that could be de- 
sired. 
If you have 
any research 
work involving 
the use of a gal- 
vanometer of high aenanivaty this instrument 
can be built to” your order, giving you the 
maximum sensitivity under your working con- 
ditions. 
We solicit correspondence from those who are look- 
ing for an out-of-the-ordinary galuanometer 
THE LEEDS & NORTHRUP CO. 
4921 Stenton Avenue PHILADELPHIA 
fhe University of California Press 
Berkeley, California 280 Madison Avenue, New York 
MOLLUSCAN FAUNA FROM SAN 
FRANCISCO BAY 
ByHoLPackard stele Calan unl iuaNeny $3.75 
Ascidians of the Littoral Zone of Southern California, by 
W. E. Ritter and Ruth A. Porsyth..........cccccsccssceeseeees 1.00 
The Subclavian Vein and its Relations in Elasmobranch 
Fishes, by J. Frank Damiel..............:csss-ccscsscssesssseseseee -10 
The San Lorenzo Series ot Middle California, A Stratigra- 
phie and Palaeontologic Study of the San Lorenzo 
Oligocene Series of the General Region of Mount Diablo, 
California, by Bruce L. Clark......:......cccccccsscceceeseeeeeenes 1.85 
New Pacific Coast Marine Algae Il, by Nathaniel Lyon 
GALTON OT ats Gets Mee eete waey seme reer ae ec ets ene 25 
Controlled Pollination in Nicotiana, by Thomas H. Good- 
speed and Pirie Davidson.............:ssscccccceeseessceeesssseesees 10 
The above titles represent Univérsity of California Publications 
in Zoology, Geology, aud Botany. Kindred series published by 
the University of California include Agricultural Sciences, 
American Archaeology and Ethnology, Entomology, Geography, 
Pathology, Physiology, Psychology. 
Complete lists of titles and prices will be sent 
on request 
A DICTIONARY FOR 
EVERY LIBRARY 
GOULD’S 
MEDICAL 
DICTIONARY 
(THE PRACTITIONER’S) 
Flexible Cloth, Marbled Edges 
Round Corners i $3.25 
(With Thumb Index, $3.75) 
71,000 Words 
Pronunciation=--Definition=-Derivation 
Includes many of the words of allied 
sciences 
P. BLAKISTON’S SON & CO. 
Publishers PHILADELPHIA 
Northrup Millivolter 
Made under the Pyrovolter Patents 
of November 6, 1917 
The new NORTHRUP MILLIVOLTER isa 
standardized portable deflection potentiometer, 
working on the Pyrovolter Principle. 
This instrument offers a convenient means 
for the accurate measurement of e m-f.s up to 
one volt, without the abstraction of any current 
from the source of the e.m.f. being measured. 
The MILLIVOLTER should generally be 
used in place of a millivoltmeter, where accuracy 
is of importance. It is valuable for taking the 
voltage drop in motors, for the measurement of 
low voltages over electrolytic baths where a 
carefully measured current is flowing, for use in 
thermocouple pyrometry, for measuring the in- 
ternal resistance of dry cells, and for accurate 
Measurement of large currents by reading the 
voltage drop over a low known resistance. 
The MILLIVOLTER has one hand-drawn 
scale and three ranges: 0-10 mv., 0-100 mv., 
and o-1000 my. It is described in Circular No. 
9, which awaits your request. 
PYROLECTRIC INSTRUMENT Co. 
Pyrometric and Electrical Precision Instriments 
636 EAST STATE STREET TRENTON, N. J. 
E. F. Northrup, President and Technical Adviser 
