The formula' for developers supplied by the makers of the plates used cannot he improved, and in nearly all cases these developers consist of pyrogallic acid and soda. The pyro-soda developer, as it is called, is admittedly the best all-round developer, and can be used for almost every kind of dry plate that is made. Pyro begins to deteriorate, however, directly it is mixed with water, and can not therefore be kept in solution for any great length of time so as to be reliable always for occasional itse. But if the pyro is used dry - that is, if sufficient for the plates to be developed is weighed out as required - the drawback to its use as an occasional developer is overcome. The right moment at which to stop development can only be learnt by experience. As a general rule, if when viewed by transmitted light the shadows are beginning to veil over, the plate should be removed from the developer. To determine when this veiling begins is a little difficult to a beginner, as the unaltered silver in the plate tends to give a foggy appearance to the image.

The growing picture must be carefully watched, and when it contains all the detail that is desired development may be stopped; the final print will show whether development was earned too far or stopped too soon, and it is in this way that knowledge is gained by experience. The time that elapses between the application of the developer and the first appearance of the half tones will in the case of development with a normal developer, if multiplied by 3, give the additional time in which development is complete. Thus, if thirty seconds elapse between the application of the developer and the first appearance of the half toues, development would be complete in ninety seconds more. The appearance of ' the back is important with any thinly coated plate. When the high lights show at the back of the plate, these lights can become no denser; further development can only allow the half tones to catch up, and the operator must decide how far this is desirable, and act accordingly. A good dark-room lamp with a steady flame is of vital importance, especially to a beginner, and it is sound economy to pay a fairly good price for a lamp.

The usual amateur candle lamp makes the proper judging of a plate almost impossible, and much is left to chance.