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July 20, 1883.] in the elimination of hydrogen from each, water being formed ; and the union of the halogen with the metal to form a salt. Ex amples :— 1. HCI+K(HO)=KCI+H,O 2. H280++Ca(HO)=CaSi+2H,0 ACTINIC FOCUS.—Sec Lenses. ACTINISM is the term which has been given by Mr. Hunt to that principle of the solar spectrum which produces the pheno mena of chemical change. It has been contended that neither the force which causes the sensation of light, nor that which produces the phenomenon of heat, has very decided chemical action, and, consequently, we are driven to the hypothesis of the existence of a new form of force in the sunbeam, co-existing with heat and light. In order to designate this, the word actinism has been proposed. This word signifies nothing more than ray-power, and therefore, as it involves no theory, it is not open to the objections which, unfortunately, must be made to many of the scientific terms in common use. Modern investigations have, however, proved that all radiations of the spectrum produce a certain actinic effect, the locality of the maximum of actinic action depending on the nature of the sensitive body. THE EXHIBITION OF THE PHOTOGRAPHIC SOCIETY OF GREAT BRITAIN. The Exhibition of this Society, for 1883, will be held at the Gallery of the Royal Society of Painters in Water Colours, 5a, Pall Mall East, London, S.W. It will be inaugurated by a conversazione, open to members and their friends, at 8 p.m., on Saturday evening, the 6th of October. The Exhibition will remain open daily (Sundays excepted) from Monday, the 8th of October, until Thursday, the 15th of November. Admission (from 10 a.m. till dusk), one shilling. It will also be open every Monday, Wednesday, and Saturday evening. Admission (from 7 to 10 p.m.), sixpence. Members have free admission at any time, and will also be supplied with tickets to admit their friends. Season tickets will be issued : single, 3s.; double, 5s. All packing cases must be sent (carriage paid), addressed to the “ Photographic Society of Great Britain, care of Mr. James Bourlet, 17, Nassau Street, Middlesex Hospital, London, so as to arrive not later than Friday, September 28th. No packing cases can be received at the Gallery. Pictures by hand will be received at the Gallery, 5a, Pall Mall East, on Friday, Septem ber 28th, until 9 p.m. Photographic transparencies will be shown with the Society’s optical lantern on Monday evenings during the Exhibition. Slides (which must not exceed 34 inches in height) are solicited to assist this special purpose; they may be sent in, either on or before Friday, September 28th (so as to come with other exhibits before the judges of awards), or at any time afterwards during the Exhibition. Each exhibitor must send a letter of advice containing a description of each picture, as also a statement of process and any further detail, to be inserted in the Catalogue (and it is suggested that when the work shown is taken by a special process, prepared and made by the exhibitor, information as to particulars should be communicated), addressed to the “ Hon. Secretary,” Photographic Society of Great Britain, 5a, Pall Mall East, London, S.W. Each frame or picture may have the exhibitor’s name and subject neatly inscribed, but no address, or anything in the shape of an advertisement will be permitted. No pictures in Oxford frames, and no pictures previously exhibited in London, will be admitted. Photographs coloured by scientific or mechanical means will be admissible. Photographs coloured by hand will not be admitted. Photographic apparatus and appliances may be sent for exhibition. Negatives and transparencies will be admissible. The hanging committee will have the power of rejecting any pictures or apparatus forwarded. Special Notice.—By Order of the Council—The Rules and Regulations respecting the Exhibition are to be strictly adhered to, therefore no picture will be received after 9 o’clock, p.m., on Friday, September 28th. Medals will be placed at the disposal of the judges for artistic, scientific, and technical excellence, and the judges are instructed to reserve three medals for portrait or figure subjects (if they find them worthy of awards). The judges will consist of the following gentlemen The President of the Society—James Glaisher, F.R.S., &c.; three members of the Council—Captain Abney, R.E., F.R.S., Francis Bedford, Leon Warnerke ; three members of the Society—Joseph Paget, Fred Hollyer, Robert Slingsby. No charge will be made to members of the Society for exhibiting their pictures ; but to non-membere a charge of one shilling per square foot will be made for wall space ; the mini mum charge being five shillings. No charge for wall space will be made to foreign exhibitors. The charge for wall space to those exhibitors who may become members of the Society at the November meeting will be remitted. It is proposed to lay on the table a catalogue containing the price of pictures to be dis posed of ; those who wish to avail themselves of this proposal will please state the price of their pictures in the letter of advice. Notice will be sent to exhibitors when to fetch away those works which are left at the Gallery by hand, and should any exhibitor not be able to send to the Gallery, he can, by giving notice to the Assistant-Secretary, and paying the cost, have his pictures packed in a case and returned by carrier. The Council do not hold themselves responsible for any damage that may happen to the pictures, or other exhibits, whilst in their custody ; but they will take every precaution to insure their safety, and their prompt return to the owners at the close of the Exhibition. Any further information respecting the Exhibition and lantern slides can be obtained from the Assistant-Secretary, Mr. Edwin Cocking, 57, Queen’s Road, Peckham, S.E. Ooxxespondeure. “DUST IN THE EYES.LA SCREW LOOSE—OR WHAT?” Sir,—In his censorship of my letter in the June issue of the Photographic Times and American Photographer, Mr. A. L. Henderson has studiously abstained from stating that the dry plate factory which forms the subject of bis animadversion in your last number is that presided over by Mr. Samuel Fry, of Kingston. This reticence is doubt less stimulated by a fear lest, were this fact known, the purity of his motives might, especially by London photo graphers, be misconstrued. To his friends it must prove a source of regret that, at the time of writing the article, Mr. Henderson had no judicious adviser beside him to point the desirableness of paying greater attention to the truth of his premises before he suffered his genius to hurry him to such a conclusion. The account of the Kingston Dry Plate Factory was written for the American readers of the Photographic Times, who are presumed to have the sense to know that although by one of certain machines plates were seen coated at the rate of twelve per minute, it does not follow that the powers of such machines are necessarily taxed to this extent from the beginning to the end of the week. The precise language made use of by me was as follows: “ I was led by my guide to the presence of the coating machines, and saw plates being coated with emulsion at a rate perfectly astonishing, each machine turning out at the rate of sixty dozen per hour.” This deduction was made on the basis of my having timed the rate of production of one machine for about two minutes. Mr. Henderson apparently mistrusts the coating capa bilities of the machine (which is that of Eastman, of Rochester, N.Y.). I am not aware that his scepticism is of any consequence ; yet, if it conduce to the allaying of his perturbation, it is possible that a properly-couched request to Mr. Fry may afford him the opportunity of seeing, as I saw, and as 1 timed by my watch, plates coated at the rate of one in every five seconds. 1 cannot stoop to the level of the last paragraph of Mr. Henderson’s article, to notice its coarse personalities or soi disant wit, nor is it necessary that 1 should do so, for a reason that may be apparent before long; but I may say that there are others than Mr. Henderson, and whose opinions on matters appertaining to American literature and veracity are likely to carry quite as great weight as his, who have not found it necessary to indulge in sneers