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NA TURE 



[August i6, 1900 



LETTERS TO THE EDITOR. 

 \Thc Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond -with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous cotnviunications.l 



Change of Feeding Habits of Rhinoceros-birds in 

 British East Africa. 



The enclosed extract from a letter just received by me from 

 my friend, Captain Hinde, of the British East Africa Pro- 

 tectorate, will interest all zoologists. It is a curious fact that a 

 bird which is so valuable as Buphaga in clearing parasitic 

 insects from cattle that we lately agreed to give it special pro- 

 tection at the International Conference on the Preservation of 

 African Wild Animals, should now, by a sudden change of con- 

 ditions induced by man, become a dangerous and noxious 

 creature. This fact shows how difficult is the problem pre- 

 sented by the relations of civilised man to a fauna and flora new 

 to his influence. E. Ray Lankester. 



Natural History Museum, London, August lO. 



"The following case of wild birds changing their habits may 

 interest you : — The common rhinoceros-bird {Buphaga erythroe- 

 pyncha) here formerly fed on ticks and other parasites which 

 infest game and domestic animals ; occasionally, if an animal 

 had a sore, the birds would probe the sore to such an extent that 

 it sometimes killed the animal. Since the cattle plague de- 

 stroyed the immense herds in Ukambani, and nearly all the 

 sheep and goats were eaten during the late famine, the birds, 

 deprived of their food, have become carnivorous, and now any 

 domestic animal not constantly watched is killed by them. 

 Perfectly healthy animals have their ears eaten down to the 

 bone, holes torn in their backs and in the femoral regions. 

 Native boys amuse themselves sometimes by shooting the birds 

 on the cattle with arrows, the points of which are passed through 

 a piece of wood or ivory for about half an inch, so if the animal 

 is struck instead of the bird no harm is done. The few thus 

 killed do not seem in any way to affect the numbers of these 

 pests. On my own animals, when a hole has been dug, I put in 

 iodoform powder, and that particular wound is generally avoided 

 by the birds afterwards ; but if the birds attack it again, they 

 become almost immediately comatose and can be destroyed. 

 This remedy is expensive and not very effective. Is there any 

 other drug you could suggest that would be less likely to be 

 detected ? Perhaps you know that I reported three years ago 

 that these birds rendered isolation under the cattle plague regu- 

 lations useless in some districts, as I proved beyond doubt they 

 were the only means of communication between clean and 

 infected herds under supervision, a mile or two apart. These 

 birds I have never seen on the great herds of game on the open 

 plains, but I have seen them on antelope and rhinoceros in 

 the immediate neighbourhood of Masai villages, and herds of 

 cattle ; on the other hand, I have never seen the small egret 

 on cattle, though often on rhinoceros and gnu." 



Atmospheric Electricity. 



In Nature of June 14 Mr. Wilson replies to the objections 

 raised in my letter of March 29 to his explanation of the origin 

 of atmospheric electricity. Before proceeding to consider Mr. 

 Wilson's reply to my objections it may be well that the point at 

 issue between us should be clearly defined, as Mr. Wilson, in 

 my opinion, somewhat confuses it. Mr. Wilson says, " Mr. 

 Aitken contends there is no such thing as dust-free air in 

 the atmosphere." Now I certainly made no such statement, 

 for the simple reason that I do not know whether such a con- 

 dition exists to any extent or not, only a few cases being on 

 record. What I did state was, " So far as our knowledge goes, 

 it can hardly be said there is such a thing as dust-free air 

 in our atmosphere, and the cases in which low numbers have 

 been observed are so extremely rare that they can hardly have 

 any bearing on phenomena of such widespread existence as 

 atmospheric electricity, even though we suppose those few 

 particles to be afterwards got rid of." I simply asked for a 

 verdict of " not proven " against Mr. Wilson's theory. I think 

 it will be admitted that it rests with Mr. Wilson, and those who 

 think with him, to prove that the air is generally dust-free at 

 elevations higher than ordinary cumulus and nimbus clouds,- as 



without this dustless air the supersaturation necessary for 

 condensation on ions is admittedly not possible. 



Mr. Wilson discusses the question of the numlier of dust 

 particles in the atmosphere from Mr. Rankin's Ben Nevis 

 observations and my own at Kingairloch, and points out that 

 practically dust-free air has been observed on Ben Nevis. Such 

 is the case, but so far as I know dust-free air has been observed 

 on only a few occasions, and such isolated instances have 

 evidently no bearing on the case. Mr. Wilson then turns to my 

 observations and says " the mean number of dust particles in a 

 series of 258 observations, extending over nearly five years, 

 amounting to 338 per c.c. ; on one occasion the number was as^ 

 low as 16 per c.c." The above statement, it must be clearly 

 understood, refers to 258 of the tests made in the purest air, and 

 is not the mean of all the observations. In the tables there are 

 688 observations for Kingairloch : of these I find there are 41 in 

 which the reading was under 100, 341 were over a 100 but less 

 than 1000 per c.c, whilst the remaining 306 observations were 

 all over 1000 per c.c. The 16 per c.c. referred to by Mr. 

 Wilson only occurred once. In the other years referred to the 

 lowest figures were 38, 43, 67 and 205 per c.c. So that, as 

 already said, the conditions represented by those low figures, 

 such aso on Ben Nevis and 16 at Kingairloch, are so exceptional 

 that they are not likely to play any part in phenomena so 

 universal as atmospheric electricity. 



Mr. Wilson, referring to the selected observations taken at 

 Kingairloch on the pure air coming from the Atlantic, says : 

 " Air coming from such a region can hardly be considered as 

 abnormal. Moreover, such observations are necessarily made 

 in air within a few feet of the ground ; at a greater height it is 

 likely to be less contaminated." Taking the last of these points 

 first, an examination of the diagrams given along with the tables, 

 from which Mr. Wilson made his extracts, will show that when- 

 ever the air became pure the readings low down and high up 

 were nearly alike. This is shown by the curves in the diagrams 

 for Ben Nevis and Kingairloch being nearly alike during these 

 periods. Further, it may be seen from the curves that there 

 was sometimes less dust at low than at high level when the air 

 came from the Atlantic. 



An examination of the tables from which Mr. Wilson took his 

 Kingairloch figures easily refutes his assumption that the air of 

 the Atlantic, as given in these tables, "can hardly beccnsidered 

 as abnormal." In the tables will be found the results of tests 

 made in France, Italy and Switzerland. Observations were 

 made at three places in France on the shores of the Mediter- 

 ranean, at Hyeres, Cannes and Mentone. An analysis of the 

 figures for these places, made during visits extending over five 

 years, shows that the lowest number observed was 725 per c.c, 

 and of eighty-eight tests only ten were under 1000 per c.c, the 

 others being all "over 1000. At the Italian Lakes observations 

 were made at Bellagio and Baveno. Many of these observations 

 were made at elevations up to 2000 feet. In all, 188 tests were 

 made : of these the lowest was 300 per c.c. On only thirteen 

 occasions was the number under 1000, and 175 readings gave 

 numbers over 1000 per c.c. 



Perhaps it may be objected that all these Continental tests- 

 were made in low level polluted air. We shall therefore^ now 

 examine the result of the observations made on the Rigi Kulm, 

 given in the same tables. The top of the Rigi is 5900 feet above 

 sea-level, but it has only the purifying effect of 4400 feet, as it is 

 only about that height above tho surrounding plains. During 

 the tests, made on the visits during the five different years pre- 

 viously referred to, 259 observations were taken on thirty-two 

 days, and the lowest number observed was 210 per c.c. Ninety- 

 seven observations gave readings under 1000 per c.c, whilst the 

 other 162 tests were all over 1000 per c.c. These tests, at both 

 high and low level, give no support to Mr. Wilson's statement 

 that the Atlantic air on the west coast of Scotland " can hardly 

 be considered as abnormal." 



Let me further support this point by reference to observations 

 made by others of the air in different parts of the world. Prof. 

 G. Melander, of Helsingfors, in his work, entitled " Sur la: 

 condensation de la vapeur d'eau dans I'atmosphere," gives the 

 results of 268 tests made of the air at Saleve, Biskra, Torhola, 

 Loimola, Kristianssund and Grip. In all these 268 samples of 

 air tested there were only five with less than 500 per c.c, and 

 no low numbers were observed. 



I now turn to the very interesting series of observations made 

 by Mr. E. D. Fridlander and published in the Quarterly 

 Journal of the Royal Meteorological Society, vol. xxii. No. 99, 



NO. 1607, VOL. 62] 



