August 24 1905J 



NA TURE 



397 



those termed English include several varieties of foreign 

 origin which are commonly grown in England. In most 

 cases the trees were on the crabstock : — 



117 English 



36 Scotch 



9 Irish 



8 French 



(i German 



7 Russian 



May 64 

 May 89 

 May 9-4 

 May 9-0 

 May 4-0) 

 Mav 8-6 



Another point of some interest in connection with these 

 results may be mentioned, namely, that there is a con- 

 nection between the earliness of blossoming and the earli- 

 ness of the ripening of the fruit, though it is so slight 

 that it becomes apparent only when the averages of a 

 considerable number of varieties are taken, and fnany 

 individual instances may be noticed where the later fruit 

 follows the earlier blossoming : — 



37 Early varieties 



40 Mid-season varieties 



40 Late varieties 



... May 4-7 

 ... Mav 6-3 

 ... May 80 



This letter, 1 fear, is already too long, but it leaves un- 

 mentioned several points which may be of importance 

 in determining the fruiting of trees. 



Spencer Pickering. 



Artificial Diamonds. 



Of the two phases, diamond and graphite, diamond is 

 the denser, and has also the less internal energy. It 

 follows that, if carbon can be crystallised at comparatively 

 low temperatures, the minimum pressure sufficing to de- 

 termine the diamond form will be lower than that 

 employed in M. Moissan's experiments. 



For estimating the transformation temperature corre- 

 sponding to low pressures, the data available are incom- 

 plete ; it is here suggested, however, as a tentative result 

 from experiments which are still in a preliminary stage, 

 that the transformation temperature corresponding, to 

 atmospheric pressure lies somewhere between 550° C. and 

 700° C., or not far outside those limits, temperatures 

 having so far been judged only by eye. 



A molten alloy of lead with about i per cent, calcium 

 appears to be capable of holding in solution some small 

 proportion of carbon, which exists either as free carbon 

 or as calcium carbide ; 

 and if the calcium is 

 eliminated from the molten 

 mass, some carbon 



crystallises out. Steam, 

 for example, converts the 

 calcium into hydrate with- 

 out attacking the lead. 

 If the reaction has 

 occurred at a full red heat, 

 graphite is found in the 

 crust of lime ; if only a 

 very low red heat has 

 b^en attained, no graphite 

 is found, but a number of 

 very small or microscopic 

 crystals, which have many 

 of the properties of the 

 diamond. The illustration 

 is from a pencil drawing 

 of a very minute crystal, viewed under a magnification 

 of 80 diameters, and drawn on a greatly enlarged scale. 



The crystals obtained exhibit mostly faces of the octa- 

 hedron, modified by the cube and dodecahedron ; in no case 

 has any internal flaw or lack of perfect transparency been 

 detected in them. The refractive index is clearly very 

 high, and an attempt to determine it by displacement of 

 focus gave 243 (instead of 247), any 'convexity of the 

 refracting surface tending to give too low a value. The 

 crystalline faces are, in fact, generally if not always 

 convex, in many cases strongly so. The crystals adhere 

 tenaciously to clean, dry glass; they are unacted upon by 

 ordinary acids (hot or cold), by cold hydrofluoric acid, and 

 by fused alkali at a red heat. When strongly heated on 

 NO. 1869, ^'O'L. 72] 



platinum foil, they burn away, leaving no residue. The 

 quantities at present available are too small for the ready 

 determination of density or hardness. 



Negative results were invariably obtained in control ex- 

 periments on the commercial calcium carbide which was 

 used in preparing the alloys. 



Tin may be used in place of lead, but it is freely oxidised 

 by the steam, and the resulting dioxide is troublesome to 

 get rid of. Of other reactions which appear to have 

 yielded minute crystals of diamond, the following may be 

 mentioned : — boiling benzene or toluene in contact with 

 finely powdered potassium dichromate or with concentrated 

 aqueous solution of gold chloride ; heating benzene or 

 toluene mixed with carbon tetrachloride or chloroform to 

 200° C. to 300° C. in a bomb. In the last named re- 

 actions, nearly all the carbon separates out in the 

 amorphous form, hydrochloric acid collecting under 

 enormous pressure. 



I hope shortly to return to the subject of these experi- 

 ments, and to make a fitting acknowledgment of my deep 

 indebtedness to Mr. W. J. Hartley, to Messrs. Neville and 

 Heycock, and to other friends. C. V. Burton. 



4 Chesterton Hall Crescent, Cambridge, August 19. 



The Spread of Injurious Insects. 



In 1S98 Dr. L. O. Howard forwarded to me a scale 

 insect discovered by Prof. Chaves at Ponta Delgada, 

 Azores, attacking the foliage of the orange tree. The 

 insect proved to be new, and was described as Lecaniuin 

 perlatum. Since that time it has never been reported from 

 any other place ; but now I have received some large, 

 flat, dark brown scales on orange leaves from Villa 

 Encarnacion, Paraguay, collected by Mr. Schrottky, and 

 they are this very same L. perlatum.^ This is only one 

 new case to be added to the many already known of scale 

 insects being transported from one side of the world to 

 the other, evidently by human means. It is to be regretted 

 that the British Government, with its numerous tropical 

 colonies and excellent botanical gardens, has not done 

 something to make known the scale insects within its 

 domains. It is true that Mr. E. E. Green, the Govern- 

 ment entomologist of Ceylon, is bringing out a magnificent 

 work on the scale insects of that island ; but he finds in- 

 sufficient support, and it is divulging no secret to sav 

 that the publication of this useful book will involve him 

 in very serious financial loss. There is no properlv 

 classified national collection of scale insects (the onlv good 

 collection in England is that of Mr. Newstead at Liver- 

 pool), and we are still totally ignorant of the coccid fauna 

 of many colonies. The reasons for regretting this con- 

 dition of affairs are mainly two : — (i) because in ignorance 

 pests of this group are continually being carried to new- 

 regions, where they are liable to become destructive ; and 

 (2) because man is so mixing up the distribution of these 

 insects that every year makes it more difficult to ascertain 

 their natural habitats. Having regard for the experiences 

 of the past, it is surely safe to say that the annual 

 expenditure of a few hundred pounds in the investigation 

 of these pests would be far more than repaid in economic 

 as well as scientific gains. T. D. A. Cockerell. 



University of Colorado, U.S. .A., August 10. 



A Parasite of the House-fly. 



I SHOULD like to direct attention to an interesting 

 parasite of the house-fly which is in this district extremelv 

 abundant this summer. The creature is, as a rule, very 

 hard to find, and many thousands of flies may be caught 

 in ordinary seasons without a single parasite being found 

 upon them. The animal in question is one of the Pseiido- 

 Scorpionidcs (? Chelifer), easily recognisable by its pair 

 of long chelai, and I should be glad if any of your readers 

 would inform me to what genus it belongs and whether 

 it is equally abundant this year in other places. 



Eton, August 19. M. D. Hill. 



I In my original descriplion, it is stated that the skin is not reticulateH. 

 The new material sh-iws that it is minutely reticulated or tessellate in the 

 middle of the back. The antenna;, described as S-jointed, vary to 7-joiDted, 

 with the fourth joint longest, but the third nearly'as long. 



