Oct. I, 1874J 



NA TURE 



439 



Photographic Irradiation * 



I HOPE you will allow me space to correct a slight misunder- 

 standing which has got into the present discussion on photo- 

 graphic irradiation. Mr. Crofts (Naiure, vol. x. p. 245) places 

 my views in opposition to tliose of Lord Lindsay and Mr. Ran- 

 yard. Mr. Stillman (Nature ,vo1. x. p. 381), who has given us 

 such valuable information on the molecular condition of different 

 preparations of collodion, also takes the same view. Now in 

 reality Lord Lindsay's and Mr. Ranyard's views are not opposed 

 to mine. I have simply attempted to prove that molecular 

 reflection was a cause of photographic irr.adiation, not tlial it was 

 the only aiiisc, as I quite agree with Lord Lindsay and Mr. 

 Ranyard, that the imperfections of the lens are also causes of 

 photographic irradiation, and in N.VTirRE, vol. x. p. 1S5, I 

 pointed out one form of irradiation due to the lens. But 

 the imperfection of the lens which is most fatal is that pointed 

 out by Lord Lindsay and Mr. Ranyard, namely, the inability of 

 tl>e lens to bring all the rays to a focus, whether this results from 

 the imperfections nf the outside portion of the lens, or from im- 

 jierfect achromatic * correction. No maker of lenses will tell 

 you that any lens, far less that every lens which he puts out, is 

 perfectly corrected for dispersion. Working with such an In- 

 strument, it is very clear that if we only allow an exposure suffi- 

 cient to give an image on the part of the collodion where 

 the great proportion of the rays are focused, then the photo- 

 grapliic impression will give very nearly the true boundary line. 

 But suppose we allow more light to pass through the lens, either 

 by turning the camera to a brighter light or by giving a longer 

 ex]iosure, then it is clear that the unfocused rays which gave no 

 impression when the exposure was short, will now impress them- 

 selves on the collodion, and thus the photographic impression 

 will be extended beyond the true boundary line. 



That there shouUl be difference of results in experiments on 

 photographic irradiation is quite to be expected, as there are so 

 many variables in the experiments. The light, temperature, and 

 condition of the collodion are all constantly changing, and the 

 conditions under which the experimenters work, and the appa- 

 ratus and chemicals used, are dilTerent for each experimenter ; 

 different results may therefore be expected. If the experimenter 

 u^e a good lens, and emplo/ only the central portion of it, the 

 imperfection due to the lens may be small in quantity. But if 

 his lens is imperfectly shaped and badly corrected for dispersion, 

 and he uses the full aperture, the result will be very different. 

 Again, if the expeiimcnter work with different collodions, Mr. 

 Stillman has shown that, altogether independent of the lens, a 

 very slight change in the preparation of the collodion greatly 

 alters the amount of irradiation. So far as I can at present judge, 

 the imperfections of the lens and molecular rellection are not 

 opponents, but allied enemies, which we must meet on the same 

 field. John Aiticen- 



Darroch, Falkirk, N.B. 



Can Land-crabs Live under Water? 



When in Atchin, in Sumatra, during the second Dutch expe- 

 dilion, it occurred to me to put to experimental test a statement 

 which I thought I had seen in some book or other — this book 

 turns out to be Prof. Marshall's work on "Physiology" — to 

 the effect that land-crabs are drowned when kept immersed in 

 water. 



On one occasion I kept one of these crabs under water for two 

 hours, after which time it was as lively as ever ; and on another 

 day a larger specimen was kept submerged for exactly four hours, 

 after the lapse of which time it was somewhat subdued, but by 

 no means moribund. 



Unfortunately the duration of my experiments was always 

 limited by the necessitits of ablution, as our largest receptacle for 

 fluids was a small-sized Huntley and Palmer's biscuit-tin, which 

 served as our only washing .apparatus, as well as the laboratory — 

 eventually a very leaky one — for my experiments, for a period of 

 four months spent under an equatorial sun. 



New University Club, Sept. 22 J. C. Galton 



* Wc here require some new worcf, or we must grcally extend our con- 

 ception of aclirormtism, as we liave lierc to dc.ll with rays far beyond the 

 limits of the sensitiveness of the eye ; .incl the word achromatic, as appli'-d to 

 lenses for chemical purposes, is somewhat misleading. I may here ofler two 

 suggestions as to now the imperfect power of the lens to bring all the 

 ditferent rays to a locus may be partially corrected :— (1) l^y usinp; a 

 collodion which is .as ne.-irly as possible only sensitive to those rays which t o 

 lens can bring to a focus ; or (2) by providing each lens used for making 

 accurate observations with a screen, which shall stop bact: all the rays 

 beyond the limits nhich the lens can f.xu'. 



Salivary Glands of Cockroach 



1 SEE in Nature, vol. x. p. 381, a letter on the salivary 

 glands of the cockroach, by Dr. W. Ainslie Hollis, in which he 

 remarks : — 



"As far as my experience carried me, the siccidi, the sup- 

 posed reservoirs of the saliva, never contained naturally any 

 liquid whatever, but on opening the thorax were invariably 

 found to be collapsed and empty." 



A few days ago I was observing some of these creatures. I 

 examined several shortly after they were caught ; in these the sa:- 

 culi were empty, but others which I had kept alive in a cup with 

 only a few drops of water for a day or two, had invariably the 

 sacculi distended with liquid. 



I will not attempt to explain these facts, but leave that to 

 others more capable than myself. CiiAS. Workman 



Belfast, Sept. 21 



THE AUSTRIAN POLAR EXPEDITION 



'T^HE Vienna correspondent of the Times supplies some 

 -'- interesting details concerning this important expe- 

 dition. Events have proved that there has not been an 

 expedition better fitted out, as to ship, stores, or crew, 

 than that in which this North Pole E.xpedition left 

 Bremerhavcn on June 13, 1872. 



As to the crew of twenty-four men, it was composed of 

 three naval officers, Lieutenants Weyprecht and Brosch 

 and Ensign Orel ; two engineers, and fifteen picked Dal- 

 matian sailors ; Lieut. Payer, of the Jagers, an Alpine 

 Club man, with two Tyrolese mountaineers ; Haller and 

 Kletz, and the Hungarian Kepesy as surgeon. It was 

 thus calculated for land work not less than sea work, and 

 events proved that the company had been well sorted. 



The object of the expedition being to find a north- 

 easterly passage towards the coast of Siberia, the expedi- 

 tion having arrived at Tromsoe, and having taken on 

 board Capt. Carlsen as harpooner and ice-master, started 

 on the 14th of July for the sea and the coast of Novaya 

 Zemlya. At Novaya Zemlya they met the Norwegian 

 yacht Jshjoni, in which Count Wilczek and Baron Stern- 

 berg, two of the chief promoters of the expedition, had 

 come over from Spitzbergen to establish a store for them 

 near Cape Nassau. They were for two years the last 

 human beings they saw. The stores being laid in a cleft 

 of the rocks inaccessible to the Polar bears, and the state 

 of the ice looking more promising, the ships parted com- 

 pany on the 2rst of August, the Tcgclholl go'mg north, 

 the Jsbjorn south. The hope proved to be fallacious 

 long before evening. The Jcgcthoff was icebound, and 

 irever was got out again. The temperature sank, copious 

 snowfalls cemented the loose ice-fields, and the Tcgclhojf 

 was surrounded by a solid mass of ice. 



In this precarious state the ship lay for five months, the 

 ice freezing together and bursting in turn, and so expos- 

 ing it perpetually to fresh pressure. All was prepared 

 for leaving the ship. The stores were brought on deck 

 and a portion placed on the ice. This was the most 

 trying time of the whole. Every moment the alarm was 

 sounded and the signal given for leaving the ship. It 

 was sufficient to wear out the strongest. In spite of this, 

 meteorological and other observations were carried on. 

 The strain on the mind told on the state of health in 

 spite of all precautions, and scurvy and pulmonary 

 affections set in. 



All this time the ship was being driven in a north- 

 easterly direction until, towards the end of January, 

 1873, 73 W. long, and 79 lat. were reached on February 

 25. The sun appeared again after five inonths on the 

 horizon, and on the 25th the pressure of ice ceased. A 

 massive wall had been formed round the ship, protecting 

 it from further injury. The drifting was now to the 

 north-west. Milder weather having set in, the hope re- 

 vived of setting the ship free, and for five months the work 

 went on. By dint of boring and blasting the fore part of 



