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Apparatus for Magnetic Precision Measurements

The Fahy Permeameter

Compensated Type
Developed to meet the need for a reliable and convenient apparatus
for the magnetic testing of single specimens (bars, rods, sheet ma-
terial) and for the simultaneous comparison of two similar or dis-
similar specimens. Fully described in Scientific Paper No. 306 of
the U. S. Bureau of Standards.

The Fahy Permeameter

Simplex Type
Represents a further distinct advance in the art of magnetic meas-
urements. Specially designed to test single specimens only—two
or more specimens can be compared, of course, by the results of
consecutive tests -- it fully retains the high accuracy and perfect
consistency of the compensated apparatus, but gains considerably
in simplicity of operation and speed of tests.

The Magnet-Meter An instrument developed for the precise and rapid investigation of shaped permanent magnets, such as used in magnetos, electrical measuring instruments, etc. This instrument serves to determine not only the initial strength, but also the stability of magnets.

Write for descriptive literature


Apparatus of High Quality for Magnetic and

Metallurgical Testing and Research Work Metropolitan Tower


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Marine Biological Laboratory

Woods Hole, Mass.

INVESTIGATION Facilities for reseach in Zoology,

Embryology, Physiology and BotEntire Year any. Seventy-six privato labora

tories, $100 each for not over three months. Thirty tables are available for beginnersin research who desire to work under the direction of members of the staff. The fee

for such a table is $50.00. INSTRUCTION Courses of laboratory instruction

with lectures are offered in InverteJuly 2 to August 12, brate Zoology, Protozoology. Em1919

bryology, Physiology and Morphology and Taxonomy of the Algae. Each course requires the full time of the student. Fee, $50. A lecture course on the Philosophical Aspects of Biology and Allied Sciences is

also offered. SUPPLY Animals and plants, preserved, liv

ing, and in embryonic stages. PreDEPARTMENT served material of all types of

animals and of Algae, Fungi, LiverOpen the Entire Year worts and Mosses furnished for

classwork, or for the museum. Living material furnished in season as ordered. Microscopic slidesin Zoology, Botany, Histology, Bacteriology. Price lists of Zoological and Botanical material and Microscopic Slides sent on application. State which is desired. For price lists and all information regarding material,

address GEO. M. GRAY, Curator, Woods Hole, Mass. The annual announcement will be sent on application to The Director, Marine Biological Laboratory, Woods Hole, Mass.



Professor of Botany in the University of Chicago

This study includes investigations extending over a period of fifteen years, that necessitated trips to Cuba, New Mexico, Australia, and Africa. The author studied all the genera and many of the species in the field, and preserved much material for later study in the laboratory. In addition to the data presented, the author gives an account of some of his experiences while on his tours of investigation. 186 pages, cloth; $1.50, postage extra

(weight 14 oz.)
Problems of Fertilization

Professor of Embryology and Chairman of the
Department of Zoology in the University

of Chicago A subject which has important bearings upon the problems of heredity and close relations to several fundamental biological problems. This volume is a popular presentation of the subject.

Cloth, $1.75, postage extra
The University of Chicago

Press 5811 Ellis Avenue Chicago, Illinois

Langmuir Condensation Pump

Dr. Irving Langmnir (of the
General Electric Co.) has de-
veloped an exceedingly inter-
esting and valuable bigh-speed
high-vacuum pump, and by
special agreement with the
makers, we are acting as sole
distributors, for laboratory
With this pump pressure as
low as 10-6 bar have been ob-
tained ; and there is little
doubt that very much lower
pressures oan be produced, by
cooling the bulb to be ex-
hausted, in liquid air, so as
to decrease the rate at which
gases escape from the walls.
Some type of primary pump
must be used ; capable of de-
veloping a vaonum not less

than 0.1-0.15 mm.of meroury, The illustration shows a Langmuir pamp, connected to a two-stage primary oil pump—which is operated by a HP motor ; all three parts of the outfit being assembled together on one base. JAMES G. BIDDLE

If interested, write for copy of illustrated 1211-13 ARCH STREET

Bulletin 881, issued November, 1917 ; PHILADELPHIA

and also copy of paper by Dr. Langmuir.

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SERVICE With the liquidation of the extensive Government Contracts, which we received during the war period from the Medical Departments of the U. S. Army and Navy, we now find ourselves in a position to offer our service in a prompt and unrestricted manner.


Our binding guarantee accompanies everyone of Haemacytomeler complete with FEi double chamber the Flei Blood Counting Apparatus and Flei Blood Pipettes as well, that their accuracy conforms to the specifications established by the U. S. Bureau of Standards. Test Certificates are furnished upon request.

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No. 27689

No. 27678

No. 27679 Marked improvements have been accomplished in both method of manufacture and control of the degree of fineness of the mass in the Mandler Diatomaceous Filters. Several of the largest manufacturers of biologicals in the U. S. using these Filters in very large quantities now report them as distinctly superior to those previously imported. 27689. FILTER CYLINDERS, MANDLER DIATOMACEOUS, with metallic headpiece, fitted

with lock nut, two rubber washers and one fibre washer as required for use in glass
mantles, etc., on negative pressure. Where cylinders are used on positive pressure, the
flat rubber washer and fibre washers are, of course, unnecessary.
Size, inches .

10 x 2

8x13 8x1 5x1 2 x
Each .
3.50 3.15 3.00 2.50 1.25

1.15 10% Discount in case of


72 144 144 27678. FILTER CYLINDER, MANDLER DIATOMACEOUS, 10 x 2 inches, with glazed porce

lain headpiece and nipple, for filtering acids, etc., Furnishe l in one size only.

3.50 10% Discount in case of

24 27679. FILTER CYLINDERS, MANDLER DIATOMACEOUS, with metallic headpiece with

specially long nipple. Furnished with lock nut, two rubber washers and two fibre
Size, inches .

74 x 2 6x2 Each . .

3.15 3.00 10% Discount in case of .

24 30 Complete descriptive pamphlet sent upon request

Prices subject to change without notice




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THE BOTANICAL OPPORTUNITY1 When this program was arranged, it was in tended to bring to the attention of botanists how they could serve the nation in the crisis of

Committees had been multiplied to do various kinds of necessary work. The results were not all that we had hoped for, but botan. ists were beginning to find themselves, and organization was gradually becoming more effective, because the spirit of cooperation was developing. Enough results were obtained to prove that botany could be of great service at a time of national need. The practical results were not so conspicuous to the public in the immediate activities of the war as those of chemistry and physics for example, but they were fundamental and far-reaching, looking to future as well as to present needs. We must recognize that to bring into effective cooperation great numbers of isolated, scattered, and sometimes conflicting units, takes time and a great controlling motive. But we were making progress, not so rapid as the impatient desired, but probably as rapid as human nature permitted.

Now that the emergencies of war have passed, shall we stop this kind of progress? I wish to attempt to answer this question. In doing so, I shall not formulate any plan, any scheme of organization, but shall present in brief general statement what seems to me to be our opportunity. The other speakers upon the program will doubtless present more concrete suggestions, for which I hope my statement may be an appropriate background.

In connection with the period of reconstruction, there has come to the science of botany a great opportunity, and botanists must rise to the occasion. It is a critical time for our science, for we may lapse into our former state and become submerged by more aggressive

1 Invitation paper before the joint meeting of botanists at the Baltimore meeting of the American Association for the Advancement of Science.

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