228 



NOTES AND QUERIES. 



[No. 201. 



inches, is the best difference between the two 

 points of view to produce a perfectly natural re- 

 sult ; and if the points of operation be more distant 

 from one another, as I have before intimated, an 

 effect is produced similar to what would be the 

 case if the pictures were taken from a model of the 

 object instead of the object itself. 



When it is intended that the pictures taken are 

 to be viewed by an instrument that requires their 

 distance from the eyes to be less than the focal 

 length of the lens used in their formation, what is 

 the result P Why, that they subtend an angle 

 larger than in nature, and are consequently appa- 

 rently increased in bulk ; and the obvious remedy 

 is to increase the angle between the points of 

 generation in the exact ratio as that by which the 

 visual distance is to be lessened. There is one 

 other consideration to which I would advert, viz. 

 that as we judge of distance, &c. mainly by the 

 degree oi convergence of the optic axes of our two 

 eyes, it cannot be so good to arrange the camera 

 with its two positions quite parallel, especially for 

 objects at a short or medium distance, as to let 

 its centre radiate from the principal object to be 

 delineated ; and to accomplish this desideratum in 

 the readiest Avay (for portraits especially), the in- 

 genious contrivance of Mr. Latimer Clark, de- 

 scribed in the Journal of the Photographic Society, 

 appears to me the best adapted. It consists of a 

 modification of the old parallel ruler arrangement 

 on which the camera is placed ; but one of the 

 sides has an adjustment, so that within certain 

 limits any degree of convergence is attainable. 

 Now in the case of the pictures alluded to by Mr. 

 H. Wilkinson in Vol. viii., p. 181., it is probable 

 they were taken by a camera placed in two po- 

 sitions parallel to one another, and it is quite clear 

 that only & portion of the two pictures could have 

 been really stereoscopic. It is perfectly true that 

 two indifferent negatives will often combine and 

 form one good stereoscopic positive, but this is in 

 consequence of one possessing that in which the 

 other is deficient ; and at any rate two good pictures 

 will have a better effect : consequently, it is better 

 that the two views should contain exactly the same 

 range of vision. Geo. Shadbolt. 



Frotonitrate of Iron. — "Being in the habit of 

 using protonitrate of iron for developing collodion 

 pictures, the following method of preparing that 

 solution suggested itself to me, Avhich appears to 

 possess great advantages : — 



Water - - - - 1 oz. 



Protosulphate of iron - - 14 grs. 



Nitrate of potash - - - 10 grs. 



Acetic acid - - - - i drm. 



Nitric acid - - - - 2 drops. 

 In this mixture nitrate of potash is employed to 

 convert the sulphate of iron into nitrate in place 

 of nitrate of baryta in Dr. Diamond's formula, or 



nitrate of lead as recommended by Mr. Sisson; 

 the advantage being that no filtering is required, 

 as the sulphate of potash (produced hy the double 

 decomposition) is soluble in water, and does not 

 interfere with the developing qualities of the 

 solution. 



" The above gives the bright deposit of silver 

 so much admired in Dr. Diamond's pictures, and 

 will be found to answer equally well either for 

 positives or negatives. If the nitric acid be 

 omitted, we obtain the effects of protonitrate of 

 iron prepared in the usual way. John Spilleb." 

 (From the Photographic Journal.') 



Photographs in natural Colours. — As " N. & Q." 

 numbers among its correspondents many residents 

 in the United States, I hope you will permit me 

 to inquire through its columns whether there is 

 really any foundation for the very startling an- 

 nouncement, in Professor Hunt's Photography, of 

 Mr. Hill of New York having "obtained more 

 than fifty pictures from nature in all the beauty 

 of native coloration," or whether the statement 

 is, as I conclude Professor Hunt is inclined to 

 believe, one of those hoaxes In which many of our 

 transatlantic friends take so much delight. 



Matter-of-Fact. 



Photographs ly artijiciul Lights. — May I ask 

 for references to any manuals of photography, or 

 papers in scientific journals, in which are recorded 

 any experiments that have been made with the 

 view of obtaining photographs by means of arti- 

 ficial lights ? This is, I have no doubt, a subject 

 of interest to many who, like myself, are busily 

 occupied during the day, and have only their 

 evenings for scientific pursuits : while it is obvious, 

 that if such a process can be successfully prac- 

 tised, there are many objects — such as prints, 

 coins, seals, ohjects of natural history and antiquity — 

 which might well be copied by it, even though 

 artificial light should prove far slower in its action 

 than solar lisht. A Clerk. 



JR^pIie^ to iMtn0r <!h\itxiti. 



Vandyke in America (Vol. viii., p. 182.). — I 

 would take the liberty of asking Mr. Balch of 

 Philadelphia whom he means by Col. Hill and 

 Col. Byrd, "worthies famous in English history, 

 and whose portraits by Vandyke are now on the 

 James River ? " I know of no Col. Hill or Byrd 

 whom Vandyke could possibly have painted. I 

 should also like to know what proof there is that 

 the pictures, whomsoever they represent, are by 

 Vandyke. Mr. Balch says that he favours us 

 with this information " in answer to the query " 

 (Vol, vii., p. 38.) ; but I beg leave to observe that 

 it is by no means " in answer to the query," which 

 was about an engraved portrait and not picture, and 



