May 28. 1853.] 



NOTES AND QUERIES. 



533 



to the appointed number of churches, and at each, 

 taking the ring of the church door in his hand, 

 repeated the oath. 



One of the most curious specimens of the 

 practice of swearing men by that to which they 

 attached most importance, is to be found in an 

 Hindoo law. It says, let a judge swear a Brahmin 

 by his veracity ; a soldier by his horses, his ele- 

 phants, or his arms ; an agriculturist by his cows, 

 his grain, or his money ; and a Soudra by all his 

 crimes. John Thbupp. 



Surbiton. 



I know nothing about judicial oaths : but the 

 origin of the form Mil. Bbeen states to be used by 

 the Roman Catholics of the Continent, and the 

 Scotcli Presbyterians, may be seen in Dan. xii. 7. : 

 " When he held up his right hand and his left 

 hand unto heaven, and sware by him that liveth 

 for ever." And in Eevelation x. 5, 6. : " And 

 the angel . . . lifted up his hand to heaven, and 

 sware by him," &c. See also Genesis xiv. 22. 



Maria. 



PHOTOGBAPHIC COBKESPONDENCE. 



Washing Collodion Pictures — Test for Lens. — 

 As I was indebted to the kindness of Db. Diamond, 

 amongst otiier friends, for my original initiation 

 into the mysteries of photography, it may appear 

 somewhat presumptuous in me to differ from one 

 \vho has had so much more experience in a point 

 of practice. I allude to that of ivashing the collo- 

 dion negative after developing, previously to fixing 

 with the hyposulphite of soda ; but, probably, the 

 reasons I urge may have some v/eight. As the 

 hyposulphite solution is intended to be used re- 

 peatedly, it appears to me not advisable to intro- 

 duce into it any free acid (which must occur if 

 the negative be not washed, although the quantity 

 at each operation may be small), because it causes 

 a decomposition of the salt, setting free sulphurous 

 acid, and also sulphur ; which last is slightly solu- 

 ble in the hyposulphite of soda, and thus the sul- 

 phur is brought in contact with the reduced silver, 

 and forms a sulphuret of that metal. But the 

 change does not stop here : for, by the lapse of 

 time, oxygen is absorbed, and thus a sulphate of 

 silver is formed, and the colour changed from 

 black to white. That sulphur is set free by the 

 additiion of an acid to the solution of hyposulphite 

 of soda, is a fact so easily demonstrable both to 

 the eyes and nose of the operator, that no one 

 need remain long in doubt who is desirous of 

 trying the experiment. 



A correspondent desires to know how to test 

 the coincidence or otherwise of the visual and 

 actinic fool of a combination : this Is very readily 

 accomplished by the aid of a focimeter, which can 

 be easily made thus : 



Procure a piece of stout card-board, or thin 

 wood covered with white paper, on which draw a 

 considerable number of fine black lines, or cover 

 it with some fine black net (what I believe the 

 ladies call blond), which may be pasted on. Cut 

 up the whole into a dozen good-sized pieces of 

 any convenient form, so that about four square 

 inches of surface at least be allowed to each piece. 

 Paste over the net a circular or square label about 

 the size of a shilling, bearing a distinctly printed 

 number one on each piece, from 1 upwards ; and 

 arrange the pieces in any convenient manner by 

 means of wires inserted into a slip of wood ; but 

 they must be so placed that the whole can be seen 

 fi'om one point of view, although each piece must 

 be placed so that it Is one inch farther off from the 

 operator than the next lowest number. Having 

 placed the camera eight or ten feet from the cards, 

 carefully focus to any one of the numbers, 4 or 

 5 for Instance ; and observe, not that the number 

 Is distinct, but that the minute lines or threads of 

 the net are visible : then take a picture, exposing 

 it a very short time, and the threads of the card 

 bearing the number that was most perfectly In 

 focus visually ought to be most distinct ; but, if 

 otherwise, that which Is most distinct will not only 

 show whether the lens is over or under corrected, 

 but will indicate the amount of error. If under 

 corrected, a lower number will be most distinct ; 

 if over corrected, a higher. Geo. Shadbolt. 



Test for Lenses. — I beg to submit to a Countet 

 Peactitioneb the following very simple test for 

 the coincidence of the chemical and visual foci of 

 an achromatic lens : 



Take a common hand-bill or other sheet of 

 printed paper ; and having stretched It on a board, 

 place It before the lens in an oblique position, so 

 that the plane of the board may make an angle with 

 a vertical plane of about thirty or forty degrees. 

 Bring any line of type about the middle of the 

 sheet into the true visual focus, and take a copy 

 of the sheet by collodion or otherwise. Then, if 

 the line of type focussed upon be reproduced 

 clearly and sharply on the plate, the lens is cor- 

 rect ; but if any other line be found sharper than 

 the test one, the foci disagree ; and the amount of 

 error will depend on the distance of the two lines 

 of type one from the other on the hand-bill. 



J. A. Miles. 



Fakenham, Norfolk. 



Improvement in Positives. — I have great plea- 

 sure In communicating to you an improvement in 

 the process of taking positives, which may not be 

 uninteresting to some of your readers, and which 

 ensures by far the most beautiful tints I have yet 

 seen. I take three ounces of the hyposulphite of 

 soda, and dissolve it in one pint of distilled or rain 

 water ; and to this I add about one or one and a 

 half grains of pyrogallic acid, and seventy grains 



