The Optical Magic Lantern Journal (July 1892)

86 The Optioal Magic Lantern Journal and Photographio: Enlarger. | Correspondence. THE LIFE OF A GAS CYLINDER. [Zo the Editor.] Srr,—Every user of gas in cylinders, especially oxygen, aust have noticed the presence of what would appear to be a powder of some sort in the cylinder itself. This is no doubt nothing more or less than oxide of iron (rust), caused by the action of the oxygen on the metal, the effect being to gradually eat away the interior of the cylinder, till a time when re-charging would be attended with danger. Now, Sir, it would, to my mind, be a desirable thing if this subject were discussed, and it would also be interesting to know what may fairly be considered the average life of an oxygen gas cylinder. Will any of your more-experienced contributors kindly state their views on this subject 1—Yours faithfully, Ryde, Isle of Wight. INQUIRER, A FREE GIFT TO ALL LANTERNISTS. [Lo the Editor, } Dear Sir,—I have had some very attractive lantern slides (coloured) sent me from the following manufacturers, which are forwarded to all lanternists who make application for them, carriaye paid :— 1, Watson and Sons, Soapmakers, Leeds. 2. Cadbury Brothers, Bournville, Birmingham. 3. Bird and Sons, Monufacturers, Birmingham, I am sure all your readers who make the application will be pleased with the gift, as they are made from very attractive show-cards. It would be conferring a favour upon your numerous readers (as it is not generally known that the above-named slides are presented to all who apply for them) if you would put this in your issue for July. I thank you, asa lanternist, for the help I have received through your popular Lantern Journal.—lI am yours truly, T. CHELLEW, Yeovil. ILLUMINATED FOUNTAIN, [Zo the Editor. } DEAR Sir,—I thank you for asking Mr. Stocks to write. I have shown his letter to friends, and one is ordering a lamp by this mail. I recently asked a friend who was on a visit to England to ascertain if anything was obtainable for showing the effect of the illuminated fountain on a small scale either by light through a fountain, or by light through the water in reservoir, or to the fall of water therefrom. My friend could not hear of any fountain or apparatus for the effect. I should be glad to know if you happen to have heard of a dealer who kept such stock. If so, a note in your Journal giving name of maker and prices, would I think be acceptable to your readers, as it is one of the prettiest effects that can be produced by the lantern. It has often struck me that s:me small perpetual fountain could be devised at smal! cost, or a small apparatus made for showing the effect on the dropping water which could be profitably sold by dealers at a small cost.— Yours truly, JAMES CALLENDAR, Christchurch, N.Z., 18th May, 1892, 20% THE subject of saturators appears to be of great interest to our readers, and we will have some further communications in our next issue. SEVERAL correspondents are informed that thereareno | conditions respecting who may or may not try for the prize mentioned in last issue. It is open to all (professionul and amateur), and slides may either be photos or sketches, 1 { Notes and Queries. J. I, C.—Have repeated as desired. : G. S. asks where he can obtain a quantity of hard lime in therough. Amsmve,—From inquiries we have made we understand that it may be obtained at the pits in Surrey, but it is useless to write there aboutit. The only way seems to be to attend personally, when any amount may be had for a trifle. Quick,—We have not used the Anschutz Instantaneous Camera, Write to the Blackfriars Photo. Co.,1, Surreyrow, S.E,, and they will send you full particulars. A. T. Hare.—We will look forward to the arrival of the promised particulars, — Showman writes :.‘‘Is it possible for the same individual to work a bi-unial and give the accompanying lecture at thesame time?” Ansner.--Yes, we have often seen the same person fill both offices ; but it will be evident that the party should be quite familiar with the lecture, for it is impossible to keep strictly to the text. F, Kirkness writes : “Is it absolutely necessary, when using a bi-unial lantern furnished with blow-through jets, that a bye-pass be used for the oxygen side of the jet? The reason why I ask is that a friend tells me that Mr. Hepworth says it cannot be used without.” Reply.— Your friend must be mistaken, B. B.—(1) The weight of asteel cylinder to hold twelve feet of gas would be somewhere about 12lb. (2) The shield for the lime cylinder may be obtained from Mr. Wood, of Cheapside, E.C. . Th, Roberts,—The style of lens you speak of is a good one, but we are inclined to think the price a fancy one. Rev. S. G. Poole (Ontario) writes: ‘I read an article from your Magic Lantern Journal, respecting a new saturator for the lantern; where can it be obtained?” Ans, —The inventor is Mr. Lawson, Rectory View, Newtonle-Willows, Lancashire. We have sent your letter to him: doubtless he will write you. or FW. Holland (New Zealand).—Your communication ve chromo-litho pictures, had been sent to Messrs. Theobald, of Farringdon-road, who say they will communicate with you at once. J. H, writes; “ Will you kindly through ‘Notes and Queries,’ give me a little information to the two following queries :—(1) I have a new gas bag, which leaks so badly, that gas should last two hours, does not last a third of that time, Can you kindly inform me where I can send it to haveit seen to, as I cannot find out the leak myself? (2) How is the focus of a lens determined? A book { have says that to geta 12ft. picture, with a lens of tin. focus, I should be 9ft. from the screen. Can you tell me how to find the focus of the lens? Reply: (1) Any local shop where mackintoshes are sold would be able to repair the leak ; if you could repair it yourself, the position of leak can readily be ascertained, by dipping any suspected corners under water when the bag is full, and watching for air bubbles.—(2) What book did you read such nonsense in? We would like to seeit. The distance required would be 16ft., and not 9ft., as stated. You will find full particulars of relative distances in a table we published in page 41 of this Journal for Oct., 1890. To find the focus, hold the lens a short distance from a sheet of paper fastened say on the wall of a room opposite the window ; move the lens to or from until distant objects are quite distinct on the paper. The distance from the paper to that part of the lens where the stop goes is the focus. Amateur writes: “ What is themeaning of FS, F16, &c. with regard to the stops for a lens, and how amI to know the relative sizes?" -nsver.—Supposing a lens to have a focus of Sin., a stop having an aperture of oneeighth of the focus, or lin., will be FS ; while one of onesixteenth of the focus, or }in., will be F16,