e Prism-Dioptry to the Meter Angle.
The Relation of the Prism-Dioptry to the Lens-Dioptry.
The Perfected Prismometer.
The Prismometric Scale.
On the Practical Execution of Ophthalmic Prescriptions involving Prisms.
A Problem in Cemented Bi-Focal Lenses, Solved by the Prism-Dioptry.
Why Strong Contra-Generic Lenses of Equal Power Fail to Neutralize
Each Other.
The Advantages of the Sphero-Toric Lens.
The Iris, as Diaphragm and Photostat.
The Typoscope.
The Correction of Depleted Dynamic Refraction (Presbyopia).

_Press Notices on the Original Edition:_

OPHTHALMIC LENSES.

"The work stands alone, in its present form, a compendium of the various
laws of physics relative to this subject that are so difficult of access
in scattered treatises."--_New England Medical Gazette._

"It is the most complete and best illustrated book on this special
subject ever published."--_Horological Review_, New York.

"Of all the simple treatises on the properties of lenses that we have
seen, this is incomparably the best.... The teacher of the average
medical student will hail this little work as a great boon."--_Archives
of Ophthalmology, edited by H. Knapp, M.D._

DIOPTRIC FORMULAE FOR COMBINED CYLINDRICAL LENSES.

"This little brochure solves the problem of combined cylinders in all
its aspects, and in a manner simple enough for the comprehension of the
average student of ophthalmology. The author is to be congratulated upon
the success that has crowned his labors, for nowhere is there to be
found so simple and yet so complete an explanation as is contained in
these pages."--_Archives of Ophthalmology, edited by H. Knapp, M.D._

"This exhaustive work of Mr. Prentice is a solution of one of the most
difficult problems in ophthalmological optics. Thanks are due to Mr.
Prentice for the excellent manner in which he has elucidated a subject
which has not hitherto been satisfactorily explained."--_The Ophthalmic
Review_, London.

The book contains 110 Original Diagrams. Bound in cloth.

Price, $1.50 (6s. 3d.)

PUBLISHED BY THE KEYSTONE,
THE ORGAN OF THE JEWELRY AND OPTICAL TRADES,
19TH & BROWN STS., PHILADELPHIA, U.S.A.

* * * * *

OPTOMETRIC RECORD BOOK

A record book, wherein to record optometric examinations, is an
indispensable adjunct of an optician's outfit.

The Keystone Optometric Record Book was specially prepared for this
purpose. It excels all