June I, 1888.] 



SCIENTIFIC NEWS. 



513 



EXPERIMENTS W^ITH THE 

 LANTERN. 



MAGIC 



IN a former article we pointed out the value of the 

 magic lantern as a teaching appliance, and advocated 

 the use of slides to illustrate history, geography, etc., 

 which can be easily prepared by the average amateur 

 photographer. But the lantern is not only serviceable 

 for the exhibition of pictures and diagrams, for it can be 

 turned to excellent use as a means of showing actual ex- 

 periments. Its power of magnification is its chief value 

 in this service. There are hundreds of experiments 

 ■wfhich cannot, by reason of the small area to which they 

 are confined, be effectively exhibited before a number of 

 spectators. Should a teacher or lecturer attempt to per- 

 form one of these, he has to report the results by word 

 of mouth to his hearers. He tells them that he has 

 just done such and such a thing, and he now observes 

 that such and such a result is becoming visible. But 

 the audience want to see the result for themselves, and 

 unless they can do so the value of the demonstration is 

 altogether lost. Let us cite as an example of this a well- 



FlG. I. 



known experiment — the electrolysis of water. The 

 usual requirements for this experirrent consist of a 

 vessel of acidulated water containing two inverted tubes, 

 also filled with the same liquid, and each of which covers a 

 piece of platinum foil. These slips of foil are connected 

 with the electrodes of a batterj^, consisting usually of 

 two or three Bunsen cells. Directly connection is estab- 

 lished with the battery bubbles rise from the platinum 

 slips, and the gases evolved from the decomposition of 

 the water are collected in the tubes. Those who are 

 close to the lecture table have no difficulty in watching 

 the progress of the experiments, but to those in the 

 background it is almost invisible. But let this experi- 

 ment be transferred to the lantern, and the images of 

 the two tubes are shown six or eight feet long, and every 

 bubble of gas which traverses the water which they con- 

 tain is visible to every one of a large audience. Of 

 course a special form of slide is necessarj', containing 

 two tiny tubes, which can easily be connected with a 

 battery cell outside the lantern. The experiment under 

 these circumstances is on such a tiny scale, although it 

 appears so large, that a single bichromate cell is quite 

 sufficient for the purpose. It is our intention in these 

 articles to show how apparatus for this and other ex- 



periments can be easily contrived by those who have a 

 little mechanical ingenuity. 



It is a pity that makers of lanterns generally do not 

 provide appliances for the ready performance of experi- 

 ments. In certain German models which we have seen, 

 the space between the condensing lens and the objective 

 is left entirely open, instead of being closed in as is the 

 case with English lanterns. This space is occupied by a 

 kind of table, which can be adjusted to any height, and 

 the image of anything placed thereon is projected upon 

 the screen. The possessor of any lantern which is 

 furnished with a separate three or four wick lamp, can 

 easily construct for himself, or have made by a carpenter, 

 an addition which will at once enable him to perform 

 all kinds of experiments. This simple contrivance is 

 shown at fig. i. 



AA is a base-board about one foot in length, and slid- 



FiG. 4. 



Fig. 5. 



ing in to it is another smaller board A", which carries 

 the upright C. B is a fixed and similar upright, screwed 

 down to AA. L is the mineral oil lamp as usually sup- 

 plied to lanterns, and which can be purchased separately 

 if desired. The two dotted lines across the upright B 

 show the position of a circular hole which is destined to 

 receive the condensing lens, while a similar but smaller 

 hole in C holds the objective D. Any one already in 

 possession of a j-plate photographic portrait lens can 

 use this as the objective, with the certaintj' that it will 

 give a good result. The two projections on B are milled 

 screws, which can be adjusted to hold slides of different 

 thicknesses, close to the condensing lens. In using this 

 contrivance the slide is roughly focussed by moving A' 

 in or out, as the case may be, while the fine adjustment 

 is represented by the rack and pinion on the front lens. 

 We have little doubt that any lantern maker would 

 carry out these ideas if he were instructed to do so, but 

 others, who are able to use carpenters' tools, will be in- 

 dependent of his services. 



A great number of experiments possible with the 



