NEW

Leitz Microscope Lenses

A "Periplan Oculars"

These eyepieces represent a new series to
Replace the Compensating Oculars

The "Periplan Eyepieces" serve to eliminate the curved image obtained with microscope objectives and to overcome the attending defects so readily noticeable towards the periphery of the image. Due to this important feature the "Periplan Eyepieces are recommended for use with Apochromats and high power Achromatic Objectives in preference to other oculars.

FEATURES: 1. Flatness of field to the periphery of image-most important for Micro-Photography.

2. Increase in size of image (up to 50% and over).

These Eyepieces are available for an initial magnification of 4x, 5x, 6x, 8x, 10x, 12x, 15x, 20x and 25x. Price from $4.00 to $6.00 each.

WRITE FOR PAMPHLET No. 0-1024

B Fluorite Oil Immersion Objective "1/7a"

N. A. O. 95, Focal length 3.45 mm.

Due to the use of fluorite lenses in place of crown lenses, the features of color correction and increase in light are noticeable to a very high degree. Aside from the crisp definition we do not want to overlook mentioning that the flatness of field is most remarkable.

FEATURES: 1. Quick change from a medium power objective to a high power Oil Immersion.

2.

3.

The use of coverglasses of increased thickness.

Especially recommended for use with Darkfield Condenser.

4. High Efficiency for Micro-Photography and Projection. Price $32.50

WRITE FOR PAMPHLET No. 0-1025

YORK NEW YORK

HAY FEVER MEMORANDA

"

SERIES II

Late Spring Type. Patients whose hay fever develops
in the latter part of May, or during June, should be tested with
the pollens of the chief grasses, such as orchard grass, timothy,
red top and certain early flowering weeds.

Late Summer Type. Patients whose hay fever develops in
mid-August and continues until frost should be tested with the
pollens of such weeds as ragweed and goldenrod, the related
sunflower; also with the pollen of the one important late
flowering grass, viz., corn, if exposed to same.

ARLCO-POLLEN EXTRACTS

For Cutaneous Tests and Treatment cover early and "late spring, also Summer and Autumn.

For service that requires exceeedingly "fine" and uniform current regulation, we offer the following rheostats:

15" long 4" wide

5" high

$12.50

20" long 5

wide

6' high

$25.00

60 blocks" thick
3' square

22" long 7" wide
7 high

$50.00

60 blocks" thick

4'' square

22" long 8 wide
9" high

Price on application

*This rheostat is supplied with three movable terminal plates, as shown in the picture.
Write for Bulletin No. 937, describing "Jagabi" Laboratory Rheostat
1211-13 ARCH ST., PHILADELPHIA

JAMES G. BIDDLE

Headquarters for

Assay, Bacteriological and Chemical Labora

tory Apparatus

Also for

Chemical Reagents, Minerals, Drugs and Stains

Amongst our leading apparatus specialties we mention the following: Chainomatic, 2J and Student Balances; Dulin Rotarex and other forms of asphalt testing apparatus; U. S. Weather Bureau Barometers; Emerson and Parr Calorimeters with accessories; Campbell, Hurley, Du-Bosc, and Kober Colorimeters, also Lovibond Tintometers; Braun Braun Chipmunk Crushers and Disc Pulverizers; Barnstead and Stokes Water Distilling Apparatus; Juerst Ebullioscopes; Braun and Kimley Electro Analysis Apparatus; Bailey, Pickel and Soxhlet Extraction Apparatus; Replaceable Unit Organic, Combustion, Muffle, Crucible, "HeviDuty" and " High-Temp" Electric Furnaces; Orsat, Hempel, Elliott, Haldane, Henderson, Rogers, Tuttle, and Williams Gas Analysis Apparatus; Detroit Gasoline Gas Generators; Gauges; Beamué, Brix Specific Gravity, and Twaddle Hydrometers; Bausch & Lomb and Spencer Microscopes and Microtomes; Bausch & Lomb Metallurgical Outfits, also Wysor Grinding and Polishing Machines; Hortvet Cryoscope and Morgan Drop Weight Apparatus; DuPont Nitrometers and Kjeldahl Apparatus; Abel Pensky and Pensky Martin Flash Point Testers; Doolittle, Engler, MacMichael, Sayboldt and Stormer Viscosimeters; Bingham and Green Viscometer and Plastometer; Freas Automatically Controlled Electrically Heated Incubators, Ovens, Sterilizers, Water Baths and Water Thermostats, Eppley Standard Cells, Oil Thermostat and Electric Titration Apparatus, Polariscopes; Filter Presses, Vacuum and Pressure Pumps, Refractometers, Spectroscopes, Shaking Apparatus; Stirring Apparatus; Thermometers, Water Testing Apparatus, etc.

Du Boise Colorimeter

THIS new Balopticon will be welcomed by every institute worker or traveling lecturer. It is truly portable, yet has all the optical and mechanical features necessary to insure best projection results. The projection lens is our regular quality Balo lens; the lamp house accommodates a 400-watt Madza lamp, or special illuminant when required, and condensers are of full 4 inch diameter.

The case, of leatheret-covered wood, is an integral part of the outfit, shutting off light flare and serving as a supporting base for instrument in operation. The equipment is unusually well balanced, making it very easy to carry.

Write for booklet on this new Balopticon.

Bausch & Lomb Optical @.

Leading American Makers of Photographic Lenses, Microscopes, Projection Apparatus
(Balopticons), Ophthalmic Lenses and Instruments, Photomicrographic Apparatus, Range
Finders and Gun Sights for Army and Navy, Searchlight Reflectors, Stereo-Prism
Binoculars, Magnifiers, and other high-grade Optical Products