Since writing you last, I learn from a friend who is intimate with Mr. McLachlan that there is every possibility of his secret being revealed ere long. That this secret formula will be an immense boon to all photographers, there can be little doubt. If an absolute immunity from streaks in the direction of the dip, brain-markings, and pinholes--which are the advantages said to be derived from the process--can be guaranteed, then will the manipulatory part of photography be at once made easy; and Mr. McLachlan will have conferred a personal obligation on every photographic manipulator. Not only will photographers be benefitted by Mr. McLachlan's generous conduct, the whole world will participate in the advantages he intends to place as a gift in the hands of photographers; and even _art_, that is so afraid of a photographic amalgamation, will be _honoured_ by the revelation. But once let the mind of the operator be for ever free from the cares and anxieties of his negative being clean, spotless, and excellent in quality, he will then have more time and inclination to put his art knowledge, if he have any, into practice, by paying more attention to the pose of his sitters and the artistic choice and arrangement of accessories. If he be without art knowledge he will be obliged to acquire it and put it into practice, or be driven out of his field of operations. For, if the chemical difficulties and uncertainties are to be so summarily disposed of, and all the manipulations reduced to a certainty and dead level, a pre-eminence in the profession can only be maintained by him who exhibits a taste, feeling, and love for his labours superior to the desire to palm upon the public, for mere gain, works that are a disgrace and a scandal to the profession of which he is a member. That such a condition of things photographic may be quickly brought about is much to be desired, and if such be the result of Mr. McLachlan's very noble willingness to give to the photographic community experiences that have cost him much time and money in acquiring by close observation and experiment, he will, at the least, be entitled to the sincere and hearty acknowledgments of all well-wishers and lovers of our art-science. _Apropos_ of clean and easy development, I should like to know if any of your numerous readers have tried the effect of sulphate of zinc with the iron developer. I understand its use obviates the necessity of using acetic acid as a retardant; that the deposit of silver is much more delicate than that produced by iron alone; that the control over it is very great; that any amount of intensity can be obtained by one or more applications, without the aid of pyrogallic acid, and without producing harshness or hardness. With such recommendations it is certainly worth a trial. I have had no time to try it myself, but think it is of sufficient importance to give your readers an opportunity of experimenting with it, and judging for themselves.