276 



KNOWIJ I )(".!■:. 



JiM.v, 1912. 



remarkable, boiiin cinlit -jointed, exclusive of the division 

 of tlu- tarsus wliich has one long and six siiort joints in 

 addition to the claws. These, like those of the second and 

 third pairs .ire also jointed near the ends. Three out of the 

 four joints nearest the body has-o five curious fan-shaped 

 organs suspended from them by flexible stems which connect 

 them with the tracheal and nervous systems. These are the 

 malleoli, and measure about 1-7 millimetres across in the 

 widest part. The convex lower edge of each fan is bordered 

 with fine vertical striae about 2-5 ^ apart. We have no 

 knowledge as to the functional use of these appendages. 

 Preparations and micro slides of Solpiiga were exhibited in 

 illustration of the paper. 



Mr. A. E. Conrady, F.R.M.S., made " Some remarks on 

 experiments on alternative microscopical theories." 



ORNITHOLOGY. 



By Hugh Bovd V\^\TT, M.H.O.U. 



WHITE STORK (C/CO.V/.l ALBA) NESTING IN 

 CAPTIVITY. — Hitherto, lliu only records we have of this 

 bird rearing its young in captivity in this country are from 

 Kew Gardens in the years 1902 and 1903. In the Zoological 

 Gardens, London, last year (1911) four eggs were laid and 

 one bird hatched out. which did not survive. This year five 

 eggs were laid and they have all been hatched out and, it is 

 hoped, that some, at any rate, of the young may be successfully 

 reared. 



THE BRITISH BLACK-BACKED GULL.— Dr. Percy 

 R. Lowe has separated the Larus fusciis of Linnaeus into 

 two races, which he proposes to name Larus fuscus fusciis 

 and L. fuscus hritannicus. The last named is a new sub- 

 species and, according to Dr. Lowe, sufficiently distinguished 

 as a more western or light-backed race from the Scandinavian 

 or more eastern, dark-backed form, to justify the opinion 

 he has arrived at (British Birds, June 1912, Vol. IV, pages 

 2-7, with a platel. 



THE BREEDING RANGE OF THE FULMAR IN THE 

 BRITISH ISLES.— In the last two numbers of the Scottish 

 Xaturalist (May and June, 1912. pages 97-102 and 121-1321 

 Dr. J. A. Harvic-Brown gives a detailed and informative 

 account of the extension in recent years of the breeding 

 quarters of the Fulmar [l^ulinarus glacialis) on our northern 

 coasts. The species has been long known as nesting in great 

 numbers on St. Kilda, there being continuous historical 

 evidence of this extending back for some two hundred and 

 fifty years. A remarkable feature of this station was its 

 isolation, none other being found nearer than Iceland and 

 Spitzbergen, until the year 1838, when a settlement was made 

 on the Faroes. On St. Kilda the numbers of the birds have 

 considerably increased, but Dr. Harvie-Brown leaves it open 

 to question whether those now nesting at other places came 

 from St. Kilda or from more northern regions, or from both ; 

 and he also leaves for future discussion the probable cause or 

 causes of the widespread colonisation which has taken place. 

 In chronological order that process may be summarised as 

 follows: — In 1878 Foula was occupied: in 1886-7, North 

 Rona and Sulisgeir ; in 1889, Stack; from 1891 onwards, 

 various places in Shetland, nearly twenty being now frequented 

 in this group of islands; in 1897, near Cape Wrath and in 

 1900-1 Dunnet Head (both on the Scottish mainland) ; from 

 1900 onwards, several places in Orkney; in 1902, Fair Isle, 

 Flannan Islands, Handa, and Barra Head; in 1910, Shiant 

 Islands; in 1911, Berriedale Head (Caithness) and in the same 

 year Ireland was reached and Ulster and Mayo populated. 

 Of the localities named only Ireland and Barra Head are 

 south of St. Kilda, and all the places are smallish islands 

 except the two in Ireland and three in Scotland. 



It is interesting to recall that Darwin, in " The Origin of 

 Species," says that the Fulmar is the most numerous bird in 

 the world, but the grounds or authority for the estimate are 

 not given. 



I'lio roc.R Ai'in'. 



By Edgar Senior. 



REVERSAL OF THE PHOTOGRAPHIC IMAGE.— In 

 order to obtain a perfect negative of the sut)ject being photo- 

 graphed, it is necessary that the exposure should be as correct 

 as possible, over-exposure resulting in a flat and often very 

 foggy image, while when still further prolonged " to a sufficient 

 extent," causing a reversal of the first effect of the light action. 

 Reversal, then, in its most complete form results in the forma- 

 tion of a positive, instead of a negative image upon develop- 

 ment, or while the greater portion of the image may be 

 negative, the rest will be positive, owing to the great difference 

 in brilliancy between the objects photographed. An example 

 of this kind is seen when including the image of the sun in a 

 landscape, an exposure sufficient to bring out detail in the 

 near foreground producing a reversal of the sun's disc. The 

 cause of this phenomena can scarcely be considered as 

 thoroughly established, owing chiefly to the uncertainty which 

 exists as to the nature of the alteration brought about when 

 light changes silver bromide in a gelatine plate into a develop- 

 able condition. Experiment, however, has shown that the 

 image, "as far as development is concerned," can be destroyed 

 by quite a number of agents. .Mmost anything that will readily 

 part with oxygen will doit; hence such substances as perman- 

 ganate of potash, potassium bichromate, any of the ferric 

 salts, ozone, peroxide of hydrogen are effective. There is 

 still one other substance which has a destructive action upon 

 exposed silver bromide and that is bromine. If a plate that 

 has been exposed to light is treated with bromine water, the 

 image will be destroyed. Its presence during exposure is 

 accounted for on the hypothesis that it is liberated by the light's 

 action, although it is an open <|uestion whether any halogen is 

 set free during a normal exposure. There appears little doubt, 

 however, that something of this nature does occur during a 

 very prolonged one, and it only remains as to the length of 

 time that must elapse before this change commences. In any 

 case it has been shown that if a gelatine or other plate be 

 soaked in a strong solution of sodium sulphite or potassium 

 nitrite no reversal will occur during an unlimited exposure 

 to light. These experiments therefore form strong evidence 

 in favour of the argument that bromine in some way is the 

 cause of the trouble. If the halogen acts in such a manner 

 that it reconverts back to its original state the light-altered 

 compound, its behaviour furnishes an example of reversible 

 chemical action in which the products of the reaction will under 

 certain conditions react with each other to re-form the original 

 substance. As an example we may take the case of the 

 preparation of hydrogen by the passing of steam over 

 red-hot iron, when a reaction expressed by the equation 

 Fes + 4 H-j O = Fes O* + Hs occurs, but it is equally true 

 that if Fea Oi and hydrogen are heated together the reaction 

 expressed by this equation occurs ; — Fea Oj + H,. = Fes + 

 4 Hi O. Now under certain conditions either of these 

 reactions may be carried to approximate completion, but 

 if iron and steam be heated together in a closed vessel the 

 iron will never be completely oxidised, because as soon as any 

 Fea Oi and H are formed they tend to react with each other 

 to re-form Ho O and Fe, in other words the reaction is 

 reversible, or can take place in either direction at the same 

 time, and may be represented as follows : — 



Fe + 4 H.i O 



:^ Fes O, + H„ 



It has. however, been shown that under certain conditions the 

 whole of the iron can be completely oxidized as expressed by 

 the equation Fes + 4 Hj O = Fes O, + H», the conditions 

 being that the hydrogen shall be removed from the sphere 

 of action as fast as it is formed. In order to do this a 

 large excess of steam over that shown in the e(iu.ation is 

 necessary, in order that the hydrogen may be swept away 

 and so prevent it converting back to its original state some 

 of the product of the first reaction. On the assumption 

 then, that bromine is set froe by the action of light we have 

 an analogous case, in which the halogen will, unless removed, 

 react with the altered silver salt, or it may be enter into com- 



