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1862. aciddt etardio is no™ cessW rite 15 whicb2 PP^ er ith bo there 8 .tire b sharadk. ous bo-) throng gh30 be m ery pl xperieb, deis " and p d perW eengivd y afier’ oticed . t to shof sen mt,) mesaod! the bath ly filu ' n vario violent * ""r Ice., k vhich " or ten • Amet pr 1orou ,03 , imu acid.® ing Mt iter. dry" le wit., of co" raporatj If alcob" Iree de" ■i * o. 1, 5 cs M plasses w 1 quan"! toed llodiop’ THE PHOTOGRAPHIC NEWS. 309 JUNE 27,1862.] table of proportions and distances on both SIDES OF LENSES FROM THE POINT WHICH IS THE ZERO OF MEASUREMENT. BY M. CLAUDET, F.R.S.* A. B. A. B. 100- 1- 20- 5- 90-90 1-10 19-60 5-10 82-83 1-20 19-23 5-20 76-92 1'30 18-86 5-30 71-40 1-40 18-51 5.40 66-66 1-50 18-18 5-50 62-50 1-60 17-85 5-60 58-82 1-70 17-52 5-70 55-55 1-80 17-24 5-80 52-63 1-90 16-96 5-90 50- 2- 16-66 6- 47-61 2.10 16-39 6-10 45-45 2-20 16-13 6-20 43-47 2'30 15-87 6-30 41-66 2-40 15-62 6-40 40- 2-50 15-38 6-50 38-46 2-60 15-15 6-60 37-03 2-70 14-92 6-70 35-71 2-80 14-70 6-80 34-44 2-90 14-49 6-90 33-33 3- 14-28 7* 32-26 3-10 14-08 7-10 31-25 3-20 13-88 7-20 30-30 3-30 13-69 7-30 29-41 3-40 13-51 7-40 28-57 3-50 13-33 7-50 27-77 3-00 13-15 7-60 27-02 3-70 12-98 7-70 26-81 3-80 12-82 7-80 25-64 3-90 12-65 7-90 25- 4- 12-50 8- 24-39 410 12-34 8-10 23-80 4-20 12-19 8-20 23-25 4-30 12-04 8-30 22-72 4-40 11-90 8-40 22-22 4-50 11-76 8-50 21-74 4-60 11-62 8-60 21-27 4-70 11-49 8-70 20-83 4-80 11-36 8-80 20-40 4-90 11-23 8-90 11-11 9- 9-09 11 •. 10-98 9-10 8-28 12 ' 10-87 9-20 7-69 13 10-75 9-30 7-14 14 10-63 9-40 6-66 15 10-52 9 50 6-25 16 10-41 9-60 5-88 17 10-31 9-70 5-55 18 10-20 9-80 5-26 19 10-10 9-90 5* 20 3-33 30 10- 10- 2-50 40 ---- 2- 50 The quantities A and B 1-66 60 "re the factors of the same 1-42 70 Poduct, which is always 100; and one being given, 1-25 80 111 90 e other may be found by 1- 100 Riding 100 tty known. by the quan- te We take the column A for the distance of the negative, ta column B will indicate the proportion of enlargement and d; —tance of trance of the the image. If we take the column B for the negative, the column A will indicate the reduc- - and the distance of the image. See M. Claudet’s “Rule for Finding Distances,” p 282, No. 198. COLLODION FOR NEGATIVES. The conditions of a good negative collodion are: 1. That it must possess the properties of intensity to a considerable degree. 2. That it must possess good flowing qualities in order to obtain an even and structureless film. 3. That it must have body to give a negative of sufficient density. To secure these qualities it is necessary to use the purest chemicals that can be obtained. The pyroxyline or soluble cotton has more to do with the excellence of collodion than any other ingredient, and great care must be used in testing and selecting an article which will best answer. A good article of soluble cotton is harsher to the touch and shorter in the fibre than ordinary cotton. If it is very short and powdery it may have considerable solubility, but it is apt to give a film full of opaque spots, and is unsuitable for collodion. If it docs not differ much in texture from ordi nary cotton, it is not sufficiently soluble, and should also be rejected. The criterion of good pyroxyline is, that it should possess the maximum of solubility, and at the same time give a transparent film when poured upon glass and allowed to dry. If an article can be found which will dissolve in the proportion of eight grains to the ounce in the mixture of ether and alcohol, and give a perfect homogeneous and transparent film, it may generally be relied upon as a good article for negative collodion. No sample should be used which makes a film too thick after dissolving six grains to the ounce in the alcohol and ether. Pyroxyline which exhibits a glutinous appearance in dis solving, will flow in a slimy manner on the plate, and is not fit for use. The best cotton will fall slowly to the bot tom in the alcohol and ether, and will dissolve with libera tion of beautiful air-bubbles, with little or no appearance of glutinosity. It should leave no flocculent matter, and deposit but a very slight sediment on standing. It is necessary to observe also that the soluble cotton should be quite free from acid when it is used. Pyroxyline, when it is kept for some time in close stoppered bottles, partially decomposes, forming oxalic acid. It may, moreover, be found in an acid condition from imperfect washing in the process of manufacture, so that the acids used are not tho roughly cleansed from it.—Humphrey's Journal. • Correspondente. A HINT TO PHOTOGRAPHIC TOURISTS. Dear Sir.—Having recently paid a visit to the Isle of Man, it has struck me as a very singular thing, that photo graphic tourists seem to ignore the existence of a place possess ing so much interest and beauty. In passing through the streets of London, no one can fail to observe that the views from the Isle of Wight, Jersey, Guernsey, and many places of much less interest, arc abun dant, while views of that fine old historical relic, Peel Castle, or the beautiful picturesque town of Douglas, are nowhere to be seen. That it does not arise from paucity of subject I can my self testify, for in my humble opinion the Isle of Man affords more variation and boldness of scenery than the Isle of wight, and almost every nook and corner of the latter place are familiar to all the little shoeblacks of the Strand. Peel Castle is quite as interesting as Tintern Abbey, but, as I before observed, that is not to be obtained, while to get a fresh view of Tintern Abby is almost impossible ; uidess some enterprising photographer where to engage the services of Mr. Coxwell, and even then I should doubt its origin ality. Again, I might compare Douglas and Ryde, but, Mr. Editor, I will leave your much more able pen to assign a reason and suggest a remedy for this, contenting myself