GENEKAL PBELIMINAKY PBEPABATIONS 201 



has taken place in the quality of the illumination. This may 

 best be done by putting a plate into an ordinary dark-slide, 

 withdrawing the shutter half-way, and exposing the plate to the 

 dark-room light for a minute or two ; on development, no 

 difference should be noticed between the part of the plate 

 which has been exposed to the light and that shaded by the 

 dark-slide shutter. 



It is desirable that the dark-room should be kept at as 

 regular a temperature as possible. The variation between 

 summer and winter is so great that unless some means of 

 regulating the temperature is adopted the time taken to 

 develop plates will vary within very considerable limits ; further, 

 the sensitiveness of the plates themselves would appear to be 

 affected to a marked degree, so that one and the same plate 

 would require somewhat more exposure during winter than 

 during summer. The situation of the dark-room, therefore, 

 should if possible be such that it is not subjected to great 

 differences of temperature, and the necessary conditions can 

 best be obtained if the room is in the basement of a house, and 

 has a northern aspect. 



A good water-supply is essential, and the tap should give 

 an easy flow, and be provided with a rose to give a fine spray of 

 water if so desired. 



It is convenient to have an arrangement for rocking the 

 dish during the process of development, and if a slow developer 

 is being used, it is then quite practicable to place the plate in 

 the developer, cover the dish so that it is protected from light 

 from the dark-room lamp, and start the rocker, leaving it for 

 a few minutes for development to commence. There are many 

 rockers, simple and otherwise, on the market ; but a perfectly 

 efficient one may be improvised by anyone with but a small 

 knowledge of carpentry. 



Take a piece of any hard wood about 8 in. by 6 in. by 1 in. and 

 on one of its longer edges screw firmly in a direction at right 

 angles to its surface a strip 3 in. by 1 in., and about 3 ft. 

 long. At the middle-line of the first -mentioned piece of wood 

 which supports the dark-room dish, put in two round-headed 

 screws, one on either side, so that if the arrangement is now 

 placed on the dark-room bench it is free to rock on the heads 

 of these screws, allowing the long strip of wood to hang over 



