5^4 



KNOWLEDGE & SCIENTIFIC NEWS. 



[November, 1906. 



ever conclusive they may appear to be. A theory of 

 reversal naturally includes, or is a part of, the theory 

 of the character of the thing reversed, that is the 

 developable image, and this is a large subject. 

 Reversal, as well as the developable condition, appears 

 to be producible by any form of energy, but it has been 

 found that the reversibility of the developable image 

 depends upon the method by which the developable 

 condition has been produced, as well as the method by 

 which the action is supplemented in order to get re- 

 versal. These observations are referred to more at 

 length in this Journal for August, 1904, and seem diffi- 

 cult, if not impossible, to reconcile with the theory that 

 so many are satisfied with at the present day, namely, 

 that the changes are simply chemical, the developable 

 image consisting of a reduction product of the silver 

 bromide, and reversal being a process of oxidation. 



Smoking Sensitive Paper for 'Recording Instru- 

 ments. — Referring to the method of using sensitive 

 paper in self-recording instruments that I described two 

 months ago, Mr. Thomas Bolas, in the Amateur 

 Photographer, says that : " The operation of smoking 

 the paper is an extremely delicate one, but when done 

 successfully the film of carbon is uniform, grainless 

 even under a high power microscope, without tendency 

 to scale off, and so thin as to give a bare line or tracing 

 without roughness. In smoking paper it must be held 

 by two opposite edges, so as tO' stretch the sheet on a 

 metal surface, this surface being a portion of a cylin- 

 der. .\ broad-wicked paraffin lamp mav be used for 

 smoking, or, better still, a number of small pieces of 

 camphor laid in a row and lighted." 



Photographing Medals, Coins, etc. — The well-known 

 similarity between the representation of a sunk and a 

 raised design is taken advantage of by M. E. Demole 

 (Coniptcs Rcndus, 1906, cxlii., 1409), in the photographv 

 of such things as medals. .\n impression of the article 

 is obtained in dull lead foil, and the concave side of 

 this is photographed under oblique illumination directly 

 on to bromide paper, without the use of an intervening 

 negative, the double lateral reversal giving an un- 

 reversed print. ITie details of the operation are not 

 further described. 



Picture Post-Cards. — The postal facilities accorded to 

 " picture post-cards " are equally, available for any form 

 of pictorial or graphical communication, so that the 

 methods of making them may sometimes be of practical 

 scientific interest. Seeing that a good card is made by 

 sticking together a number of sheets of paper, it seems 

 to me a great waste of time and trouble to treat the 

 card as a whole, that is, to first stick the sheets together 

 and then sensitise, expose, develop, and finish the 

 photograph on the card, when the photographic work 

 would be more quickly and advantageously done on the 

 outer sheet of paper before it was stuck to the others 

 to form the card. For the photographic sheet, ordin- 

 ary bromide or other printing paper might be used, and 

 when the " picture " is completed it might be made 

 into a card by sticking the necessary paper sheets at 

 the back of it. The paper bearing the photograph and 

 the other sheets that go to make up the card should 

 all be rather larger than required, and the whole finally 

 trimmed to size. I do not know whether trade printers 

 of picture post-cards adopt this method, but it appears 

 to offer many advantages. 



A Long-Lost Beetle. 



Non equidtiii invideo, miror magis. 



One day in Septeml>er last four persons might have 

 been seen on a Surrey common, turning up spadefuls 

 of the heath-clad sand, and scrutinising them with 

 eager eyes and fingers. " Treasure seekers," said the 

 passers by, and they were right; but we were prospect- 

 ing after no vulgar treasure. Three of us, it should be 

 said, were amateurs, the fourth was an insectarian of 

 note. 



Two hundred years ago, the great Sir Hans Sloane 

 discovered on Hampstead Heath, and added to the 

 British fauna, a strange beetle, captured parasitic in a 

 nest of the " Bloody Ant " (Formica sanguinea). It was 

 duly chronicled, described, exhibited at a meeting of 

 the lately founded Royal Society, and received the name 

 of Lomechusa strumosa. It may be seen to-day in the 

 museum, side by side with a second specimen unac- 

 countably taken soon afterwards in the Mail Coach 

 between Gloucester and Cheltenham., This was in 

 1 710; until now no third example had been noted; it 

 came to be looked upon as dubious or extinct, and has 

 long been omitted from the published lists of British 

 species. 



Towards the end of July in this year, the long-lost 

 in.sect was re-discovered by an enthusiastic coleopterist, 

 and it was under his guidance that we were rummaging 

 the clods. He failed on this occasion to unearth 

 Lomechusa; but he showed us several mounted speci- 

 mens from the former find, and we were rewarded by 

 meeting with another extraordinarily rare beetle, resem- 

 bling a tiny crocodile, and known as Dinarda dentata. 

 The " Bloody Ant " nests in old fir-stumps, or burrows 

 into banks, concealing its nest with grass. It is a slave 

 holder, carrying off in their pupa state, and training 

 to obedient servitude, the young of Formica fusca. 

 Lomechusa is fed by its hosts; they obtain from it, in 

 turn, a sweet secretion, which deteriorates the nursing 

 instincts of the workers, causing pseudogynes, or false 

 queens. It is constant to F. sanguinea, being never 

 found in nests of the adjacent large " Wood Ant," 

 Formica ruia. 



To a humanistic student, the genus specialist is not 

 less interesting than are to himself the prizes of his 

 own research. Our friend, we found, was not a 

 riaturalist, not an entomologist, not even a coleopterist, 

 all our general questions as to Hampton Court spiders, 

 male wasps, death watches, he smilingly put by. Of 

 beetles inhabiting ants' nests, and of their entertainers, 

 he knows what is to be known, and lives in hopes of 

 knowing more ; all other knowledge he shuts out. 

 Some day, I suppose, this micromania will exhaust 

 itself; there will be no tiny worlds to conquer, no more 

 quiddities to reveal; we shall admire, instead of classify- 

 ing, shall once more see Nature whole, shall revert for 

 the. poetry, the power, the picturesqueness of zoology, 

 to the pages of a Buffon, a Linneeus, a Gilbert White. 



W. M. T. 



