_Head-rests._--The difficulty I have experienced in getting my children to sit for their portraits in a steady position, with the ordinary head-rests, has led me to design one which I think may serve others as well as myself; and I therefore will describe it as well as I can without diagrams, for the benefit of the readers of "N. & Q." It is fixed to the ordinary shifting upright piece of wood which in the ordinary rest carries the semicircular brass against which the head rests. It is simply a large oval ring of brass, about an inch and a half broad, and sloping inwards, which of the following size I find fits the back of the head of all persons from young children upwards:--five inches in the highest part in front, and about four inches at the back. It must be lined with velvet, or thin vulcanised India rubber, which is much better, repelling grease, and fitting quite close to the ring. This is carried forward by a piece of semicircular brass, like the usual rest, and fixes with a screw as usual. About half the height of the ring is a steel clip at each side, like those on spectacles, but much stronger, about half an inch broad, which moving on a screw or rivet, after the sitter's head is placed in the ring, are drawn down, so as to clip the head just above the ears. A diagram would explain the whole, which has, at any rate, simplicity in its favour. I find it admirable. Ladies' hair passing through the ring does not prevent steadiness, and with children the steel clips are perfect. I shall be happy to send a rough diagram to any one, manufacturers or amateurs. J. L. SISSON. Edingthorpe Rectory. _Sir W. Newton's Explanations of his Process._--In reply to MR. JOHN STEWART'S Queries, I beg to state, First, That I have hitherto used a paper made by Whatman in 1847, of which I have a large quantity; it is not, however, to be procured now, so that I do not know what paper to recommend; but I get a very good paper at Woolley's, Holborn, opposite to Southampton Street, for positives, at two shillings a quire, and, indeed, it might do for negatives. Secondly, I prefer making the iodide of silver in the way which I have described. Thirdly, Soft water is better for washing the iodized paper; if, however, spring water be made use of, _warm_ water should be added, to raise it to a temperature of sixty degrees. I think that sulphate or bicarbonate of lime would be injurious, but I cannot speak with any certainty in this respect, or to muriate of soda. Fourthly, The iodized paper should keep good for a year, or longer; but it is always safer not to make more than is likely to be used during the season. Fifthly, If I am going out for a day, I generally excite the paper either the last thing the night before, or early the following morning, and develope them the same night; but with care the paper will keep for two or three days (if the weather is not hot) before exposure, but of course it is always better to use it during the same day.