November 2, 191 ij 



N'ATURE 



the equator than Salisbury in Rhodesia. The importance 

 of a low latitude has been illustrated by the success of 

 Helvvan Observatory in obtaining the earliest photograph 

 of Halley's comet, owing to the longer night near Cairo 

 in summer as compared with Greenwich or Heidelberg. 

 This advantage would be still further marked in the case 

 of Khartoum, some 145° south of Helwan, or relatively 

 about as far as Barcelona is from Edinburgh. 



Altitude. — Precise determinations have been made by 

 levelling, and the land near the river has been found to 

 stand about 385 metres above sea-level. 



Climate. — So far as I am aware, the " seeing " qualities 

 of the atmosphere have not been tested. Ordinary experi- 

 ence shows that it is remarkably clear, and it is no un- 

 common thing near the Italian boundary in these latitudes 

 to see Jebel Kassala (4400 feet) and some of the Eritrean 

 hills at distances up to a hundred miles. These districts 

 are at no great height above sea-level, and the clearness 

 of vision must in large measure be due to the pureness and 

 homogeneity of the air. 



Relative humidity is a factor presumably of great import- 

 ance as regards the " seeing " qualities of the air ; and 

 those interested may refer to Captain Lyons 's " Physio- 

 graphy of the Nile and its Basin," where they will find 

 the data for Khartoum and many other stations conciselv 

 summarised. More recent data are available in the annual 

 meteorological reports, &c., published by the Egyptian 

 Survey Department. Suffice it to say that the mean annual 

 relative humidity is 31 per cent., and this figure is only 

 exceeded for three months in the year. The Khartoum 

 observations have been made within a short distance of 

 the river, and no doubt the humidity results are higher 

 than would have been obtained at a station a mile or 

 two away. The air is often dry enough, even near the 

 river, to desiccate moist calcium chloride. There are very 

 few cloudy nights. 



During the summer months violent dust-storms occur, 

 but these are generally of short duration. Situated on the 

 southern edge of the desert, it has a rainfall of about 

 6 inches a year, almost confined to the months of August 

 and September. Temperature conditions are extreme, but 

 owing to the intense dryness heat is seldom oppressive to 

 the individual. 



Communication. — Several mails a week carry letters to 

 London in nine or ten days, and the outward journey can 

 be done in eight and a half days. The railway to the Red 

 Sea enables goods from outside to reach Khartoum with 

 only a single handling at Port Sudan. 



It seems improbable that there is any other locality in an 

 equally low latitude offering the advantages of a clear, 

 dry atmosphere combined with a fair altitude and such 

 ready means of communication with European centres of 

 learning. As an actual site in this vicinity the Abu Meru 

 Hills may be suggested, as rising about 100 metres above 

 the river at a distance of some eight miles north-west from 

 Omdurman. The place is far enough to avoid any local 

 humidity due to the river, as well as the dust-raising 

 traffic converging on the towns. The prevalent winds are 

 from the north and north-west, and traverse hundreds of 

 miles of unbroken desert before reaching the hills. 

 _ In conclusion, I have to thank Mr. Rolston for direct- 

 ing my attention to the search being undertaken bv the 

 French Geographical Society. Our friends across the 

 Channel have extensive possessions in northern Africa, and 

 no doubt these have first claim for consideration ; but if 

 they .nre unable to exploit Khartoum, perhaps it may be 

 kept m^ view and tested when munificence can be found 

 to provide for the equipment and maintenance of a new 

 observatory. G. W. Grabham. 



Khartoum, Sudan, October 15. 



The Scientific Misappropriation of Popular Terms. 



T E\TTRT-r,Y agree with Dr. Ilarmor (Nature, October 26) 

 that (he . xh iision of priority to groups larger than genera 

 IS undrsirahlr, and tho use of tlir- word insect should be 

 judged solely by practical convcnicncf. 



If the restricted use of thf word insort wore as gonerallv 

 arcf-ptfd as that of di-i^r there would !).■ no ohlcct ion to 

 Its us,.. [ und.T-^fand, ho\\cv<r. dial \\v \\^<- of' .l-i-r for 

 small niaminals was al)aiidoncd in Middlr ICn^lish, and [ 



NO. 2192, VOL. 88] 



that the phrase " mice and rats and such small deer," 

 quoted by Dr. Harmer, was intended by Shakespeare and 

 later authors to be a joke, like the railway porter's classifi- 

 cation of the tortoise as an insect. 



The same explanation is not available for the remark 

 in Prof. Adam Sedgwick's " Text-book of Zoology " 

 (vol. i., p. 502) that " all spiders are predaceous and suck 

 the juices of other insects." 



I cannot agree with Dr. Harmer that the word insect 

 is, or ever has been, generally used in the restricted sense 

 either in popular literature or in technical works other 

 than zoological. For example, agriculturists always seem 

 to speak of insect in the wider sense, and agricultural 

 literature generally does the same. Nor do I find any 

 agreement on the subject among zoologists, and the 

 tendency seems to be for them to abandon Insecta as a 

 class name in favour of Hexapoda. Sir Ray Lankester 

 expresses the matter admirably in the new edition of the 

 " Encyclopasdia Britannica. " He rejects Insecta as the 

 class name of the "so-called 'true insects,'" and regrets 

 that Lamarck, who invented the " very appropriate name 

 Hexapoda," did not insist on it; and "so the class of 

 Pterygote Hexapods came to retain the group-name Insecta, 

 which is, historically or etymologically, no more appro- 

 priate to them than it is to the classes Crustacea and 

 .'\rachnida. " He refers with obvious disapproval to "the 

 tendency to retain the original name of an old and com- 

 prehensive group for one of the fragments into which such 

 group becomes divided by the advance of knowledge, 

 instead of keeping the name for its logical use as a com- 

 prehensive term, including the new divisions, each duly 

 provided with a new name " (Sir Ray Lankester, 

 " Encyclop. Brit.," vol. ii., 1910, p. 673). 



Those, therefore, who use the word insect in its older 

 and etymologically more correct sense have the support of 

 high zoological authorities. J. W. Gregory. 



4 Park Quadrant, Glasgow, October 28. 



The Colour of a Donkey. 



On October 5, at 7 p.m., the moon being high up and 

 almost obscured by a thick high haze, giving a diffused 

 ground light with no shadows, I was crossing an open 

 field by a footpath. The field is about a quarter of 

 a mile across, and the hedges all round it, with tall elms, 

 were marked out in broad dark masses. The grass, dried 

 by the hot summer, is straggly and grey, with short green 

 undergrowth. There were a number of cows — red and red 

 and white — scattered over the field, visible in the dim 

 light up to 80 yards by measurement. One could appar- 

 ently see everything within that radius. 



I was brought to a halt by hearing an absolutely invisible 

 animal noisily cropping the grass a few feet away. On 

 going nearer I found a grey donkey. On his starboard 

 quarter at 4 yards' distance his dark head appeared as a 

 moving blur, but " stern on " at that distance he was 

 completely invisible — an " airy nothing " — though, like 

 Polonius, " at supper." It was most extraordinary to hear 

 the animal feeding and to be unable to see a vestige of 

 him. At 2 yards' distnnce he was a mere ghost. The 

 lighter under-colour of the ventral surface certainly diffused 

 what light there was, after the manner of the vanishing 

 duck in the Oxford Museum. That may be partly the 

 explanation. 



Returning by the same path at 7.30, I tried by walking 

 across the field in every direction to find the donkey, but 

 failed, though the cows were all plainly visible, feeding or 

 lying down, and the donkey was in the field all night. 



The striped zebra, invisible in the moonlight, is cited as 

 an example of protective coloration. I merely record the 

 above facts without venturing upon any explanation of 

 them. 



There is an old rhyme describing the palpitations of a 

 villager followed at night across a field by an invisible 

 creature with audible footsteps — 



" And much he feared that dreadful ghost 

 Would leap upon his back." 



That was also a donkey, and the rhyme, liico Gil|)in's ridi\ 

 may be the jocular record of ;i {r{v\. Mv donkey was 

 ghostly enough, and suggests possiliiliiirs. 



Waterstock, October 24. E. C. Spicer. 



