July 2. 1853.] 



NOTES AND QUERIES. 



17 



Mr. Wilkinson, on the other hand, asserts that 

 3 feet in 300 yards is sufficient separation for the 

 cameras: this is only 1 in 300, — a vast difference 

 truly. 



" For views across the Thames," says the editor 

 of the Photographic Jownal, " the cameras should 

 be placed 12 feet apart, and with this separation 

 the effect is declared to be astonishing." 



Mb. Wilkinson, however, asserts that from 4 

 to 6 feet in a mile will do well enough ! 



Farther, Mr. Latimer Clark (the inventor of an 

 ingenious stereoscopic camera) states that with 

 regard to the distance between the two positions 

 of the cameras, he knows no good reason why the 

 natural distance of the eyes, viz. 2^ inches, should 

 be much exceeded. " A little extra relief is ob- 

 tained," he adds, " without visible distortion, by 

 increasing the separation to about 4 or 5 inches ; 

 but if this distance be greatly exceeded, especially 

 for near objects (I give the gentleman's own 

 words), they become apparently diminished in 

 size, and have the appearance of models and dolls 

 rather than natural objects." 



The reason for making the separation between 

 the cameras greater than that between the two 

 eyes, is exceedingly simple. The stereograph is 

 to be looked at much nearer than the object itself, 

 and consequently is to be seen under a much 

 larger angle than it is viewed by the two eyes in 

 nature. Hence the two pictures should be taken 

 at the angle under which they are to be observed 

 in the stereoscope. Suppose the object to be 50 

 feet distant, then of course it is seen by the two 

 eyes under an angle of 2 J inches in 50 feet, or 1 

 in 240. But it is intended that the stereograph 

 should be seen by the two eyes when but a few 

 inches removed from them, or generally under an 

 angle of 2? in 12 inches, or nearly 1 in 5. Hence 

 it is self-evident that the stereoscopic angle should 

 be considerably larger than that formed by the 

 optic axes of the two eyes when directed to the 

 object itself. 



But there is great diversity of opinion as to the 

 extent of the angles requisite for producing the 

 precise stereoscopic or distantial effect of nature. 

 For myself I prefer Professor Wheatstone's rule, 

 1 in 25 for objects beyond 50 feet distant. For 

 portraits I find the best angle 1 in 10 when the 

 sitter is 10 feet off, and for busts about 1 in 5 

 when placed about 5 or 6 feet from the cameras. 

 But I should be happy to receive information from 

 any of your readers concerning this important 

 branch of the photographic art. For months past 

 I have been engaged in a series of experiments in 

 connexion with the subject, and wish for larger 

 experience than it is possible for any single operator 

 to acquire for himself. 



Mr. Fenton, I may observe, does not keep the 

 cameras parallel in taking landscapes, but in- 

 clines them so that the same object may occupy 



as nearly as possible the centre of the ground glass 

 plate. 



Nor is it essential that perfect horizontality or 

 parallelism of the cameras should be maintained 

 in copying trees. For buildings, however, it is 

 absolutely necessary that the cameras be kept 

 straight. 



I am sorry thus to trespass on your space, but 

 being anxious, as Me. Wilkinson says, to collect 

 information from every source, and your periodical 

 being a happy medium for conveying and re- 

 ceiving instruction, I am glad to avail myself of 

 such a channel. *. (2) 



P. S. — Mr. Claudet has, I perceive, been 

 awarded the prize given by the Society of Arts 

 for the best essay on the stereoscope. Can you, 

 or any of your readers, inform me whether this is 

 likely to be published, and when and at what 

 price ? 



Query respecting Mr. Pollock's Process. — In 

 Mr. Pollock's directions for obtaining positives, 

 which appeared in "N. & Q." (Vol. vii., p. 581.), 

 iodide of silver is to be dissolved in a saturated so- 

 lution of hypo. Can you give me the quantity of 

 iodide of silver to be dissolved, and the quantity 

 of the saturated solution of hypo, in which it is to 

 be dissolved? N. T. B. 



Gallo-nitrate of Silver. — Can you inform me 

 what the true nature of the decomposition is 

 which takes place after a short time in the gallo- 

 nitrate solution of silver? and if there be any 

 ready means of rendering the silver it contains 

 again available for photographic use ? 



Sir W. Newton, in the description of his calo- 

 type process, says : " Bring out with the saturated 

 solution of gallic acid, and when the subject 

 begins to appear, add the aceto-nitrate of silver 

 solution." Which way of doing this is the best, — 

 mixing the two solutions together and applying 

 them to the paper ; or applying the paper, when 

 wetted with the gallic acid, to the silver solution ? 



T.L. 



ViZ^liti ta i^tiwr <!k\xtxitS, 



Verney Note decyphered (Vol. vii., p. 568.). — 

 I am extremely obliged to Me. Thompson Cooper 

 for his decyphered rendering of Sir Ralph Ver- 

 ney's note of a speech or proceeding in parliament. 

 The note itself is not now in my possession, but I 

 have requested the owner to be good enough to 

 re-collate it with the original, and if any mistakes 

 should appear in the copy, or the printing (which 

 is very likely), I will give you notice of the fact, 

 that the doubtful words in Mr. Cooper's version 

 may, if possible, be set right. 



Students in the art of decyphering may be 

 pleased to have the key to the cypher recorded in 



