274 



KNOWLEDGE. 



July, 1913. 



P.fontinale. P.nitidum Jenyns(see Figure 282) still stands, 

 and Mr. Woodward points out that it has frequently been 

 mistaken for small specimens of the last species, P. personatum 

 or P. pusillum. P. personatum (see Figure 283) was recorded 

 as British by Mr. Woodward in 1908. This, again, has often 

 been confounded with other species, and its detection has 

 helped very greatly to clear matters up. P. pusillum (see 

 Figure 284), P. millium (see Figure 285), and P. pulchellum 

 (see Figure 286) still stand. P. subtruncatum was 

 identified as British by Dr. Johansen, who pointed it out 

 to Mr. Woodward in 1901 (see Figure 287). This was 

 looked upon as a variety of pulchellum by Jenyns,and is the 

 var. pallida of Jefferys' P. fontinale. P. henslowanum (see 

 Figure 288) is recognised by Mr. Woodward. P. supinum 

 was found by Dr. Johansen near Kew Gardens in 1901. Mr. 

 Woodward describes P. parvulum, which has not yet been 

 met with in Britain, and is the smallest of the Western 

 European species. P. steenbuchii, P. lilieborgii, and 

 P. hibernicum (see Figures 290 to 292) are species that were 

 not recognised till recently. P. obtusale (see Figure 293) 

 is an old friend. We figure also P. vincentianum, a fossil 

 form from the Pleistocene of Belgium, which is a new species 

 described for the first time by Mr. Woodward, but which has 

 not yet been discovered in this country (see Figure 294). 



Mr. Woodward's researches have been published by the 

 British Museum (Natural History) as a catalogue consisting 

 of one hundred and forty-four pages and thirty plates, the 

 greater part of which latter consists of collotype reproductions 

 of photographs of many hundreds of shells. In the case of 

 every species the hinges and hinge-teeth are described in 

 great detail. Symbol maps (in accordance with those agreed 

 upon by the British Association Committee for " The Forma- 

 tion of a Definite System on which Collectors should record 

 their Captures ") are also given, which show recent as well as 

 fossil records. A detailed list of localities for each species 

 is also included, and the synonomy, which in some cases runs 

 into two or more octavo pages, gives some little idea of the 

 work which Mr. Woodward has accomplished. Every 

 collector of land and freshwater shells will now have to check 

 his specimens of Pisidia and redetermine them with the 

 help of Mr. Woodward's book which can be obtained at the 

 British Museum (Natural History), Longmans, Green & Co., 

 B. Quaritch, or Dulau & Co. Price 10/6 net. w M w 



ORNITHOLOGY. 



By Wilfred Mark Webb, F.L.S., F.R.M.S. 



THE COMMITTEE FOR THE ECONOMIC PRESER- 

 VATION OF BIRDS.— We learn from the July number of 

 The Selborne Magazine that at the meeting of the Council 

 of the Selborne Society, held on November 26th, 1912, Mr. 

 Holte Macpherson and the Secretary were empowered to 

 confer with Dr. Chalmers Mitchell and others, including 

 members of the trade, as to the best steps to be taken to 

 preserve birds which are being killed off for their plumage. 

 Subsequently Mr. Macpherson, Mr. Poole, and the Secretary 

 were given formal authority to represent the Society on the 

 Committee for the Economic Preservation of Birds, to which 

 also the London Chamber of Commerce has appointed 

 representatives. Many leading zoologists have joined the 

 Committee which is now beginning active work. 



In the past, bird-lovers have sought to secure legislation 

 without stopping to consider whether the objects they seek 

 will be obtained. On the other hand the trade has occupied 

 itself with opposing all legal measures, and nothing has been 

 done. It is hoped, however — now that naturalists and 

 merchants are combining to consider the question — that some 

 steps will be taken to preserve birds whose plumage is used in 

 commerce. Anyone who has evidence to offer with regard to 

 the killing of birds for trade or natural history purposes is 

 invited to communicate with the Honorary Secretaries of the 

 new Committee, care of the Selborne Society, 42, Bloomsbury 

 Square, W.C. 



PHOTOGRAPHY. 



By Edgar Senior. 



PLATINUM PRINTING.— Of the many processes of 

 photographic printing there are few which equal in simplicity, 

 together with the beauty of the results obtainable, that known 

 as platinum printing (see Figure 27S). For while it is capable 

 of rendering shadow detail in a most perfect manner, it is at the 

 same time able to reproduce all the delicate gradations in the 

 lights. Then there is the additional advantage of permanency, 

 for which both platinum and carbon stand pre-eminent, and 

 although the former does not enjoy the advantages attending 

 the latter, of giving an almost unlimited choice of colours, 

 both warm or cold blacks and sepia are readily obtainable. 

 The papers manufactured by the Platinotype Company, 

 Gevaert Limited, and others are of several grades or kinds, 

 which refer to the surface, texture, and thickness. As the 

 paper has a great affinity for moisture, special precautions 

 have to be taken to keep it in a perfectly dry atmosphere, 

 and neglect of this is a great cause of so many failures in 

 practice. Therefore, in order to keep the paper in good 

 condition, it is sent out by the makers in sealed-up tins 

 containing a small quantity of a desiccating agent (calcium 

 chloride) which absorbs the moisture contained in the air 

 enclosed in the tin. In this manner the paper will keep 

 perfectly dry for a lengthened period, the writer having found 

 it to be in perfect condition after the expiration of two 

 years. As soon, however, as the tin is opened the paper must 

 be removed to a storage tube which is provided at one end 

 with a receptacle for containing the calcium chloride, and this 

 salt must be frequently dried and replaced in the tube ; in fact, 

 it cannot be too strongly urged upon those who use platinum 

 paper to keep their tins in a dry place, as well as keeping the 

 calcium chloride dry. If these points be attended to there 

 will not be any difficulty in preserving the paper in good 

 condition. Neglect of these simple precautions is seen in the 

 fiat, muddy, sunken-in appearance of the image. One of the 

 first considerations is the kind of negative that will give 

 the best result by this process ; it may, however, be taken 

 for granted that any negative which possesses good gradations 

 from high lights to shadows will yield a good print, but that 

 poor, flat, or thin ones will not be suitable as a rule. Before 

 commencing printing, it is necessary to dry the printing 

 frames, and especially the backs, thoroughly before a fire. 

 The negative is then placed in the frame and the coated 

 surface of the paper in contact with it, this operation being 

 conducted in as subdued a light as possible, as the 

 paper is much more sensitive than the P.O. P., and 

 the effect of short exposure to light is not apparent until 

 after the print is developed. In order to protect the paper 

 from moisture during the time of printing it is usual to place a 

 piece of vulcanised rubber upon it before placing the back of 

 the frame in position ; several sheets of waterproof paper can, 

 however, be made to answer instead. The paper before 

 exposure to light is of a lemon-yellow colour ; as the printing 

 proceeds it changes to a greenish-grey, the shadows finally 

 becoming a blue-grey and with some negatives a slight orange- 

 brown colour. It is not advisable, however, to continue the 

 printing until the detail in the lights is plainly visible. The 

 time of exposure necessarily varies with the kind of negative, 

 but it is about one third of that required for a silver print. It 

 is evident that the progress of printing can be inspected from 

 time to time ; but as over-printing is not made apparent until 

 development has taken place, some amount of experience is 

 required to know when printing should be stopped. This 

 knowledge, however, will soon be acquired after a few trials. 

 But it does constitute a vital point in the process. If thought 

 desirable, one of the many forms of actinometers may be 

 employed in printing, although they are of little use unless a 

 number of prints are required from one negative ; in which 

 case they are a help in ensuring that the printing shall 

 be carried to the same depth in each case. The printing 

 having been carried far enough, the next operation is that of 

 development. This may be carried out at once, or the 

 exposed paper may be returned to the calcium tube until a 



