ON SELF-RECORDING MAGNETOGRAPHS. 207 



practice, that with a very small share of manipulatory skill, the loss of even 

 a day's record would be impossible. 



2. Bearing these conditions in mind, on looking over the photographic 

 processes with which I was acquainted, that known as the wax-paper process, 

 first described by M. Le-Gray, seemed peculiarly applicable. In sharpness 

 it might be made to rival collodion ; and although generally stated to be slow 

 in its action, I had no doubt that its sensitiveness could be easily increased 

 to the required degree. 



Of all paper processes, I believed it to be the one most free from contrac- 

 tion, either during the time it is undergoing the action of the light, or in any 

 subsequent stage. Its chief superiority, however, consisted in its capability 

 of remaining sensitive for so long a time, that it is of little consequence 

 whether the sensitive sheets be a day or a week old. Then the comparative 

 slowness of the development, which has always been looked upon as one of 

 its weak points, would be in this case a positive advantage, as dispensing with 

 that care and attention which must always be bestowed on a quickly develop- 

 ing picture. 



In addition to all these recommendations, it was a process to which I had 

 paid particular attention, and consequently the one in which I might naturally 

 hope to meet with the greatest amount of success. 



|. The general outline of the process does not differ materially from that 

 which I published some years back in 'Notes and Queries,' vol. vi. p. 443 ; 

 but as that account was written for practical photographers, the details of 

 the manipulation were brief. It has therefore been thought advisable, that 

 while describing again the whole process, with the addition of such modifi- 

 cations as the end in view requires, I should also give such fuller description 

 of the manipulation, as may render it more serviceable to those who have not 

 hitherto paid attention to photography in its practical details. This must be 

 my excuse, if to some I seem unnecessarily prolix. None but a practical 

 photographer can appreciate upon what apparently trivial and unimportant 

 points success in any branch of the art may depend. 



It may not be without service, if, before entering into the practical details 

 of the process, I say a few words respecting the most advantageous way of 

 arranging a photographic laboratory, together with the apparatus, chemicals, 

 &c. which are of most frequent use. 



Among those requisites, which may be almost called absolute necessaries, 

 are gas, and a plentiful supply of good water, as soft as can be procured. 



4. The windows and shutters of the room should be so contrived as either 

 to allow of their being thrown wide open for purposes of ventilation, or 

 of being closed sufficiently well to exclude every gleam of daylight ; and the 

 arrangement should admit of the transition from one to the other being made 

 with as little trouble as possible. 



5. A piece of very deep orange-coloured glass, about 2 feet square, 

 should be put in the window, and the shutter ought to be constructed so as 

 to allow of the room being perfectly darkened, or illuminated, either by 

 ordinary daylight, or daylight which has been deprived of its photogrpphic 

 rayr., by filtering through the orange glass. The absorbing power of this 

 glass will be found to vary very considerably in different specimens, and I 

 know of no rule but experience to find out the quality of any particular 

 sample ; the best plan is to select from a good stock one of as dark a colour 

 as possible. The proper colour is opake to the rays of the solar spectrum 

 above the fixed line E. 



6. The best source of heat is unquestionably gas. It will be as well, how- 

 ever, to have a fire-place in the room, as, in some cases, a gas-stove will be 



