Jan. 15. 1853.] 



NOTES AND QUERIES. 



71 



picture will be ready for development before the 

 developing and fixing of the first has set its stand 

 at liberty. Cokelt. 



Mr. Crookes' Wax-paper Process (Vol, vi., 

 p. 613.). — R. E. wishes to know the exact mean- 

 ing of the sentence, "With the addition of as miich 

 free iodine as will give it a sherry colour." After 

 adding the iodide of potassium to the water, a 

 small quantity of iodine (this can be procured at 

 any operative chemist's) is to be dissolved in the 

 mixture until it be of the proper colour. 



The paper is decidedly more sensitive if exposed 

 wet, but it should not be washed ; and I think it 

 is advisable to have a double quantity of nitrate of 

 silver in the exciting bath. I have not yet tried 

 any other salt than iodide of potassium for the first 

 bath ; but I hope before the summer to lay before 

 your readers a simpler, and I think superior wax- 

 paper process, upon which I am at present experi- 

 menting. William Crookes. 



Hammersmith. 



P.S. — I see that in the tables E. E. has given, 

 he has nearly doubled the strength of my iodine 

 bath. It should be twenty-four grains to the 

 ounce, instead of forty-four ; and he has entirely 

 left out the iodine. 



India Rubber a Substitute for Yellow Glass. — 

 I think that I have made a discovery which may 

 be useful to photographers. It is known that some 

 kinds of yellow glass effectually obstruct the pas- 

 sage of the chemical rays, and that other kinds do 

 not, according to the manner in which the glass is 

 prepared. 



I have never heard or read of India rubber 

 being used for this purpose ; but I believe it will 

 be found perfectly efficient, and will therefore 

 state how I arrived at this conclusion. 



Having occasion to remove a slate from the side 

 of my roof, to make an opening for my camera, I 

 thought of a sheet of India rubber to supply the 

 place of the slate, and thus obtain a flexible water- 

 proof covering to exclude the wet, and to open 

 and shut at pleasure. This succeeded admirably, 

 but I found that I had also obtained a deep rich 

 yellow window, which perfectly lighted a large 

 closet, previously quite dark, and in which for the 

 last ten days I have excited and developed the most 

 sensitive iodized collodion on glass. I therefore 

 simply announce the fact, as it may be of some 

 importance, if verified by others and by further 

 experiment. I have not yet tested it with a lens 

 and the solution of sulphite of quinine, as I wished 

 the sun to shine on the sheet of India rubber at 

 the time, which would decide the question. How- 

 ever, sheet India rubber can be obtained of any 

 size and thickness required : mine is about one- 

 sixteenth of an inch thick, and one foot square ; and 

 the advantages over glass would be great in some 



cases), especially for a dark tent in the open air, 

 as any amount of light might be obtained by 

 stitching a sheet of India rubber into the side, 

 which would fold up without injury. It is pos- 

 sible that gutta percha windows would answer the 

 same purpose. H. Y. W. N. 



Brompton. 



Dr. Diamond's Paper Processes. — We have been 

 requested to call attention to, and to correct se- 

 veral errors of the press overlooked by us in Db. 

 Diamond's article, In the hurry of preparing our 

 enlarged Number (No. 166.). The most impor- 

 tant is in the account of the exciting fluid, — the 

 omission, at p. 21. col. 1. 1. 47. (after directions 

 to take one drachm of aceto-nltrate of silver), of 

 the words "one drachm of saturated solution of 

 gallic acid." The passage should run thus : " Of 

 this solution take one drachm, and one drachm of 

 saturated solution of gallic acid, and add to it two 

 ounces and a half of distilled water." 



In the same page, col. 2. 1. 13., " solvent" should 

 be " saturated ; " and In the same article, passim, 

 " hyposulphate " should be " hyposulphite," and 

 " solarise " should be " solarize." 



Ancient Timber Town-halls. — Since my ac- 

 count of ancient town-halls (Vol. v., p. 470.) was 

 written, one of these fabrics of the olden time 

 noticed therein has ceased to exist, that of 

 Kington, co. Hereford, it having been taken down 

 early in November last, but for what reason I 

 have not learned. Another, formerly standing in 

 the small town of Church Stretton, in the co. of 

 Salop, which was erected upon wooden pillars, and 

 constructed entirely of timber, must have been _ a 

 truly picturesque building, was taken down in 

 September, 1840. A woodcut of the latter is now 

 before me. Of the old market-house at Leo- 

 minster I possess a very beautiful original draw- 

 ing, done by IMr. Carter upwards of half a cen- 

 tury ago. J. B. Whitborhe. 



Magnetic Intensity (Vol. vi., p. 578.). — The 

 magnetic intensity is greatest at the poles ; the 

 ratio may roughly be said to be 1"3, but more ac- 

 curately 1 to 2-906. This is found by observation 

 of the oscillations of a vertical or horizontal 

 needle, A needle which made 245 oscillations in 

 ten minutes at Paris, made only 211 at 7° 1' south 

 lat. in Peru. The intensity and variations to 

 which it Is subject is strictly noted at all the mag- 

 netic observatories, and I believe the disturbances 

 of intensity which sometimes occur have been 

 found to be simultaneous by a comparison of ob- 

 servations at different latitudes. 



For the fullest information on magnetic in- 

 tensity, Adsum is referred to Sabine's Report on 



