The Optical Magic Lantern Journal (March 1897)

48 The Optical Magic Lantern Journal and Photographic Enlarger. hours; Friday, at 7, rehearsal of ‘ Athalie,”’ Concordia Society, and 8.45, Royal Polytechnic, entertainment, 1} hours; Saturday, at 2, British Museum Reading Room. been presented with the Cambridge University certificate for proficiency in the chemistry of “ Air and Water.” by Limelight” are highly appreciated and welcomed wherever they have been given, due, as his critics say, to the ‘ natural and homely accomplishments of the entertainer. They can scarcely be classed as lectures in a strict sense, intermingled as they are with song, anecdotes, and story. Songs, the quiet drollery of which is irresistible ; anecdotes of pathos, contrasting with a happy intermixture of humour, which serve to exhibit his skill in either phrase of his subject; and stories of individuals whose various eccentricities give scope for voice, gesture, and mimicry.’ And in these Mr. Rendle is very successful, his voice being clear, his style easy and natural.” His -pictures we need hardly add are for the most part works of art. Some time ago he gave a series of articles in our columns in connection with instructions for building a bi-unial. This was written at the time he was himself making one for his own use. We have since seen the completed instrument, and must say it would put to shame several so-called makers of lanterns, all the work having a specially good finish; but then he can hardly be considered-an amateur in mechanics, as the above particulars go to show. Some little time ago Mr. Rendle commenced a series of chapters in our columns termed the ‘ Tanternist’s Practical Cyclopedia.” This seems to be just one of the kinds of information that was required, and many arc the letters which we have received in connection with this, from one of which we will quote. It is from Staff-Sergt. A. J. Lawrence, P. F. Artificer, A.O.C. Gibraltar: “It is always a great pleasure to me every month to receive the Maaic LantTErRN JouRNAL, which to me is always so full of useful and practical information, which is so much to us here, I feel I must congratulate you for publishing the ‘ Lanternist’s Practical Cyclopedia,’ by your able writer, Mr. C. E. Rendle. He will have our hearty thanks for his articles, as they are just what is wanted, especially by those whose experience has been limited with the lantern: It will prove a boon to many here in Her Majesty’s Service, who manage to do a little with the lantern.” We have now said enough to give our readers some little idea of Mr. Rendle, to which we He has also j will merely add that, although of a somewhat retiring nature, he is splendid company, and one can always feel after a conversation with him that something has been learned ; also that he has a charming wife and two growing sons. | In the company of this family, it has often been Mr. Rendle’s ‘‘ Excursions j; pleasure to ourselves and family to spend a most enjoyable evening. aVr +X Wee * The Electric Light in the Optical Lantern.—No. V. By CECIL M. HEPWORTH. Fi pe term by which we measure the Wea RN pressure of electricity—it is also )\ called potential or electro-motiveforce (E.M.F.)—is the ‘‘ volt.” The stream or current is reckoned in ‘‘amperes.” The power to do work which is represented by a current of so many amperes at a pressure of so many volts, is found by multiplying the two together, when the result is called so many ‘“ Watts.” Thus, ten amperes at an E.M.F. of 100 volts—the pressure at which electricity is generally supplied commercially to the consumer—is estimated as 1,000 Watts. Another name for the same thing is a “Kilowatt,” and this quantity has been adopted by the Board of Trade as their “Unit.” Just as the gas companies reckon up your gas bill at so much per thousand feet, so the electric people charge their customers according to the number of ‘‘ units” they have absorbed. But there is another aspect of the question to be considered before we have done with the water simile. Before we can make our stream of water as pumped out by the engine do work for us, we must convey it to the point where the work is to be done by means of tubes, and we must also provide it with a return path to the pump after the work is accomplished. These tubes must be proportional in their internal diameter to the quantity of the water, or the stream will be unduly diminished if they be too small, and a large amount of the energy will be wasted before it reaches the scene of action. Also, the thickness and strength of the walls of the tubes must be proportional to the pressure on the water, or it will escape and be lost. In any case there will be a certain amount of loss