1891.] 



MICROSCOPICAL JOURNAL. 



95 



troduction of sixteen separate orders of insects, but if they investigate 

 the claims of the present vohrnie they will find that in this manner 

 they can obtain clearer ideas of the relations of the different orders than 

 by following older, although apparently less complicated classifications. 



Appletofis School Physics. By John D. Qiiackenbos, M. D., assisted 

 by A. M. Mayer, Ph. D., F. E. Nipher, A. M., S. W. Holman, 

 S. B., and F. B. Crocker, E. M. American Book Co., 806 

 Broadway, New York, 1891. 12°,, pp. 544, 408 figures. 



The editor in this valuable work on Natural Philosophy has borne in 

 mind the present demand for a text-book of the most advanced and 

 practical laboratory and pedagogical methods to be used in the higher 

 grades of high schools and academies. 



Believing that special investigators and teachers are peculiarly quali- 

 fied to represent their own branches of science, he has selected men of 

 recognized eminence and skill as assistants. The reputation of the 

 several contributors and the standing of the scientific schools which they 

 represent will secure for this work a prompt consideration and early 

 introduction to the best educational institutions. 



Attention is called to the thorough and original treatment of motion, 

 energy, and force, to the teaching not only of results but what practical 

 use can be made of them, to questions for exercising the reasoning. facul- 

 ties of the pupil and directions for simple experiments with home-m^de 

 appliances, but to us and to our readers the treatment of the microscope 

 is of especial interest, as shown by the following quotations : 



" The Compound Microscope is an instrument designed to pro- 

 duce magnified images of objects too small to be seen with the naked 

 eye. In the figure, the object a is placed just outside the principal 

 focus of a lens or combination of lenses, O. and a real magnified and 

 inverted image b c is formed. Tiiis image is then itself magnified at 

 B C by means of a simple microscope, E, called the eye-lens. The 

 latter is usually mounted in a sliding tube so that it can be properly 

 placed with respect to the image. The lens and tube together consti- 

 tute the eye-piece. If the magnifying power of O is fiftv, and that of 

 E four, the image will be two hundred times the size of life. 



" Chromatic aberration in the microscope is corrected by using a 

 concave lens in combination with the object-lens O. 



DIAGRAM ILLUSTKATING ACTION OF THE COMPOUND MICROSCOPE. 



'' As in the case of the photo-micrographic camera, the microscope 

 may be combined with the stereopticon, and illustrations of minute 

 objects thrown upon a screen for the instruction of an audience. The 



