February 4, 19 15] 



NATURE 



617 



A peine, croyons-nous, en avait-il trouv^ chez ses 

 pr^d^cesseurs un germe presque infime," etc. 



(3) For the dates of Adelard's life and writings see 

 C. H. Haskins in the English Historical Kevieiv, 

 vol. xxvi., p. 491, and vol. xxviii., p. 515 (July, 1911, 

 and July, 1913). 



(4) Adelard elsewhere in the treatise explains that 

 the earth, air, fire, and water which we see and feel 

 are not the elements earth, air, lire, and water, but 

 compounds. 



(5] The following is the complete Latin text of the 

 chapter. I have used both the printed edition in the 

 British Museum, where the text is sometimes faulty, 

 and the twelfth-century manuscript in the Eton Col- 

 lege Library, which is possibly the autograph. The 

 chapter heading reads, " Quare ex vase pleno inferius 

 aperto aqua non exeat nisi prius superius foramen 

 aperiatur." The text then begins : — 



" Adhuc mihi de aquarum naturis quiddam dubitabile 

 restat. Cum enim tempore ut scis iam preterito anum 

 prestigiosam studio incantationis discende addissemus 

 ibique anilibus imbuti sententiis nescio an sentibus 

 aliquot diebus moraremur, eadem in domo vas quod- 

 dam mirabilis efficacie ad horas prandiles afferebatur. 

 Quippe cum idem et superius et inferius perforatum 

 multipliciter foret, aqua etiam ad nianus abluendas 

 infusa, dum minister aquarius superiora foramina 

 pollice obturabat, nichil aque ab inferioribus emanabat, 

 ablato a superiore pollice statim nobis circumstantibus 

 per inferiora foramina aqua redundabat. Quod ego, 

 ipsum prestigium esse putans, quid mirum, inquam, 

 si anus dominica incantatrix est cum aquarius servulus 

 monstra pretendat. Tu vero more tuo, quoniam in- 

 cantationibus studiosus eras, minime illi rei vacare 

 dignatus es. Nunc igitur quid de aqua ilia sentis 

 aperta ; semper erant subteriora foramina et nichil 

 tamen nisi ad aquarii arbitrium fluebat. 



(A) Si prestigium id erat, nature potius quam 

 aquarum violentia id incantatum est. Cum enim 

 huius mundi sensilis corpus quatuor elimenta com- 

 ponant, ita ipsa naturali amore conserta sunt ut, cum 

 nullum eorum sine alio existere velit, nuUus locus ab 

 eis tum vacuus sit turn esse possit. Unde fit ut, 

 quamcito illorum unum a loco suo cedat, aliud absque 

 intervallo eidem succedat, neque potest a loco cedere, 

 nisi aliud quod substantiali quodam aPfectat amore 

 possit ei succedere. Clauso igitur introitu succedentis 

 frustra patebit exitus succurrentis, hoc itaque amore 

 hac expectatione in cassum aquae reperies, nisi in- 

 troitum aeri prestes. Haec enim, ut supradictum est, 

 cum non pura sint, ita coniuncta sunt ut sine se esse 

 non possint vel nolent. Unde fit ut, si in vase superius 

 penitus integro inferius fiat apertio, non nisi cum 

 intervallo quodam et quasi cum murmure liquoris fiat 

 effusio. Tantus enim aer intercedit quantum inde 

 liquoris exit, qui quidam cum ipsam aquam porosam 

 inveniat innativa sibi et tenuitate et levitate penetrando 

 superiorem vasis locum qui vacuus videtur occupat. 



Lynn Thorndike. 



The Economic Status of the Blackcap. 



In Nature of January 7 Mr. W. E. Collinge (for 

 whose work I have the greatest respect) places the 

 blackcap in his list of injurious birds. As at once a 

 gardener and an obser\'er of birds for about sixty 

 vears I wish to protest against this accusation, which, 

 if acted upon by fruit farmers, would soon lead to the 

 extinction of the most charming songster of all the 

 true warblers. 



I grant that it eats small fruits, especially rasp- 

 berries, but I contend that the insects it destroys must, 

 from the economic point of view, fully counterbalance 

 these depredations. This, of course, cannot be proved, 

 because all the insects it devours are not injurious, 



NO. 2362, VOL. 94] 



I and the proportion of these will vary in each locality, 



! but considering that the blackcap arrives in this 



country early in April and does not leave until Sep- 



i tember, while the season for small fruits lasts prac- 



I tically only from the beginning of July to the middle 



of August, we have about si.xteen weeks when it has 



to live on insects to si.x weeks of fruit eating ! 



Mr. Collinge rightly says that the bird is "not 

 plentiful" (p. 510), but adds that it has considerably 

 increased in numbers during the last eight or nine 

 years (p. 511). To this I must entirely demur — cer- 

 tainly as regards this part of Kent, where much small 

 fruit is grown. It is a bird the clear melodious song 

 of which cannot be overlooked, and as I have been 

 on the look out for it every spring for the last thirty 

 years at least, I am perhaps as competent to form 

 an opinion on this point as Mr. Collinge. I have 

 never more than one pair in my garden, and rarely 

 hear the bird elsewhere. I should say it is not as 

 abundant here now as it was twenty years ago at 

 Colwyn Bay, where I then lived. 



Alfred O. Walker. 

 Ulcombe Place, Maidstone, Kent, January 26. 



I REGRET quite as much as Mr. Alfred O. Walker 

 to have to condemn the blackcap, but in an investiga- 

 tion of this kind one must always be careful not to 

 allow sentiment or preconceived notions to bias one's 

 opinion. 



I have ample evidence that this bird has increased 

 in numbers, at least in the midland counties, during 

 the past six or seven years. I cannot speak for Kent. 

 As to the nature of its food, an examination of the 

 stomach contents of thirty-three adult and four nestling 

 birds showed that the bulk of the food consisted of 

 fruit and peas ; there were a few aphids, twenty small 

 lepidopterous larvae, and the remains of seven beetles. 

 Out-of-door observations made during the past ten 

 years add still further evidence of the injuries these 

 birds will inflict upon wall fruit, currants, straw- 

 berries, blackberries, raspberries, peas, etc. During 

 the summer of 19 13 I had ample proof in my own 

 garden of the havoc four or five birds can commit on 

 peas. 



Mr. F. Smith, of Maidstone, a large fruit-groweir 

 and a careful observer, stated in a paper published in 

 igo6 : — "A family of blackcaps in a cherry orchard 

 commit grave havoc. They do not eat a quarter of 

 the fruit they pick, and they are also very fond of 

 raspberries and figs. It is the worst summer bird we 

 have in the fruit plantations." This opinion has been 

 confirmed bv fruit-growers in all parts of the country. 



Where this species is not plentiful or in non-fruit- 

 growing districts, it may be left alone, but in fruit- 

 growing districts it should not be allowed to increase, 

 further, as I stated in 1913, "any attempt at protec- 

 tion will justify fruit-growers in taking vigorous 

 measures for extermination." 



Walter E. Coluxge. 



8 Newhall Street, "Birmingham. 



Names in Mechanics. 



In the current number of Nature Sir Oliver Lodge 

 refers to the usefulness of naming units, and many 

 of us remember what a clearing up of ideas resulted 

 in the student's mind from the substitution of the 

 term " radian " for the circumlocution " unit of circu- 

 lar measure." I wish to ascertain any names that 

 have been proposed for units in mechanics, and have 

 attained little or no vogue; as instances "velo" and 

 "celo" may be mentioned, which were proposed as 

 names for the units of velocity and acceleration. I 

 wish also to know how far Prof. Perry's " slug " is 

 in use. Can any reader of Nature help me? 



David Mair. 



