and Laboratory Methods. 2187 



LABORATORY PHOTOGRAPHY. 



L. B. ELLIOTT. 

 Devoted to Methods and Apparatus for Converting an Object into an Illustration. 



Some Suggestions on the Use of the Lantern in the 



Class-Room. 



The lantern has become one of the necessary aids in teaching, and all well- 

 equipped educational buildings are arranged for its use. By means of pictures, 

 tables, etc., projected on the screen, information can be imparted in an attractive 

 manner, and a more lasting impression made than in almost any other way. 



In spite of its evident value, however, it is not as widely used as one would 

 expect, especially in the smaller institutions. This is perhaps to be accounted 

 for by the following facts : first, because the original cost of the outfit is high ; 

 second, because of the trouble and expense of obtaining the necessary slides ; 

 and third, because the teacher usually thinks an assistant is necessary to run the 

 lantern during the class period. On account of these and other real or imaginary 

 difficulties, many high schools, academies, and colleges do not avail themselves 

 of the opportunities of this method of instruction. 



It is the purpose of this paper to point out how a lantern may be used for 

 purposes of class instruction without the expenditure of a great deal of time or 

 money. 



The Lanter-Ji Itself. A lantern is really a very simple affair. It consists of a 

 source of light, condensing lenses, a slide holder, and a projecting lens. These 

 should be attached to a base in such a way that their relative position with respect 

 to each other may be easily changed. The optical parts can be purchased from 

 almost any dealer in optical goods, and the lamp made and the various parts 

 mounted by anyone handy with tools. Where it is not desired to make a lantern, 

 a good one can be purchased cheaply from any one of the many dealers in this 

 line of supplies. A lantern should have condensing lenses four and one-half 

 inches in diameter and a projection lens whose size will depend upon the distance 

 the lantern is to be from the screen and the size of the picture desired. 



The Kind of Light. Where possible, electricity should be used. This is in 

 preference to any other form of light, since it is the most powerful and is very 

 convenient to handle. The incandescent current can be used, and this is usually 

 in modern buildings, or can be put in at very little expense. Where electricity 

 cannot be secured, the calcium light can be used, but this is usually too expensive 

 for class-room work, and acetylene or vapor light must be used. The following 

 chart indicates the candle power of the various lights ordinarily employed. 



Acetylene and vapor lights, while they do not compare with electricity for 

 brilliancy, can in reality be made to serve very acceptably in small and well 

 darkened rooms and will be sufficiently effective where the classes are small and 

 a picture over six or eight feet in diameter is not demanded. 



