April 17, 1913] 



NATURE 



161 



Whether auxetics arc necessary for any form of 

 cell-reproduction to occur is a point which will require 

 further research to determine. It is, however, a 

 striking fact that Dr. H. C. Ross was able for the 

 first time to induce divisions in human leucocytes by 

 means of auxetics, and was also able to demonstrate 

 that the ova of Ascaris megalocephala will undergo 

 division if incubated with auxetics. Dr. Fansham 

 has also shown that Entamoeba coli can be caused 

 to divide through many generations by means of these 

 substances, whilst Dr. E. H. Ross has demonstrated 

 that auxetics have a very remarkable action on try- 

 panosomes. 



From the forego' ■■■% facts it is clear that auxetics 

 are a cause_ of eel ■ eproduction, and, although we 

 cannot as vet state positively that there are no other 

 causes, yet, judging from other biological examples, it 

 ,is extremely probable that they are the sole cause, as 

 it is very unlikely that a complex function like cell- 

 reproduction should have more than one direct cause. 

 With regard to the presence of auxetics and kinetics 

 in pond water, I may say that I am at present inves- 

 tigating this point, and have definite proof of the 

 presence, not onlv of auxetics, but also of kinetics 

 or augmentors, in such waters, the latter bodies 

 apparently varying according to the season, and also 

 being dependent on the amount of albuminoid 

 ammonia present. 



Besides the presence of auxetics in hay infusion, 

 there is one further point to be mentioned, viz. that 

 if bv the action of an enzyme, the cyst-wall in Colpoda 

 were dissolved, quite enough auxetic would probablv 

 he liberated to cause division, were such necessary 

 for development. This was well shown by Dr. H. C. 

 Ross, who found that substances not themselves 

 auxetics mav vet have auxetic action by causing 

 limited cell death immediately within the walls of ova. 

 thus setting free enough auxetic to cause cell-division. 

 Aubrey H. Drew. 



6q Ewhurst Road, Crofton Park, S.E. 



Seeing how simple this proportionality factor is, 

 the work of reducing, say, McLeod gauge readings 

 to millitors will not cause any appreciable trouble, 

 whereas the indications by Prof. Knudsen in dynes/cm. 3 

 are without any reduction expressed in millitors. For 

 the highest vacua the microtor= io _: millitor = 

 0-75x10-° mm. of mercury would be convenient. 

 As abbreviations, mtor may be written for milliter, 

 Mtor for microtor. W. H. Keesom. 



Physical Laboratory, Leyden. 



Units of Pressure in Vacuum Work. 



Referring to the letter by Mr. Shaw in Nature 

 of March 20 (p. 95), I beg leave to remind readers 

 that we have already a convenient unit of pressure 

 which, as fitting in an absolute system of units, is 

 preferable to the micron of mercury, viz. the dyne 

 per cm. 2 , or the barye of the c.g.s. -system. In fact, 

 Prof. Knudsen has used it in all his later researches 

 on molecular phenomena. In article Vio of the 

 " Encvklopaedie der mathematischen Wissenschaften," 

 p. 628, note iq (Communications from the Physical 

 Laboratory at Leyden, Suppl. No. 23, p. 14), by Prof. 

 Kamerlintrh Onnes and myself, we have given prac- 

 tically the same unit under the name of niillitor as 

 convenient for such pressures as those in Rontgen 

 vacua. 



In doing this we have followed the lead of the 

 commission of the International Association of Re- 

 frigeration (Ball, de I'Ass. internat. du froid, 2, 191 1, 

 p. 38, rapporteur M. Ch. Ed. Guillaume). This com- 

 mission proposed to accept the metre-kilogramme- 

 second system for general use, this one having better 

 chances than the c.g.s.-system, and accordingly to in- 

 troduce as an absolute unit of pressure the m.k.s.- 

 unit. As a practically identical realisation of it the 

 commission proposed to introduce the international 

 centitor (abbreviated for renti-torricelli), the inter- 

 national kilotor being equal to the pressure of a 

 column of practically 75 cm. of mercury under normal 

 gravity (for further particulars see the article quoted 

 above). Practically 1 millitor=r dyne/cm. 2 , or barye, 

 and within the accuracy of experiments in the domain 

 of these vacua t millitor = o-7c y. of mercury. 

 NO. 2268, VOL. 91] 



Reflection of X-Rays and X-Ray Fringes. 



Accounts of the reflection of X-rays and of X-ray 

 fringes contributed to Nature by Messrs. Bragg, 

 Moseley, Barkla, Hupke, Keene, and others induce 

 me to send you some results that I have obtained 

 recently in the same direction. 



I think that the appearances observed by Messrs. 

 Laue, Friedrich, and Knipping are really due to the 

 same cause as the reflected spots ; they present quite a 

 similar distribution and general character. 



Fig. 1 shows the pattern obtained with a beam of 

 Rontgen rays falling at an incidence of 8o° upon a 

 face of a cube of rock-salt, the photographic plate 

 being at right angles to the reflected beam. The 

 reflected spots are similar to the transmitted spots, and 

 present fringes perpendicular to the plane of inci- 



dence ; they are situated on an elliptic curve, to 

 which belongs also the point of impact of the primary 

 beam. The spot on the main axis is regularly re- 

 flected ; the others are symmetrically disposed, and 

 possibly due to reflection on the planes of the corre- 

 sponding octahedron, dodecahedron, &c, which are 

 in suitable positions. Fluorine gives the same pattern. 



Fig. 2 is obtained with a beam (incidence 8o°) 

 falling upon the triangular face of an octahedric crystal 

 of magnetite. The reflected spots show two systems 

 of fringes, one of which is approximately perpen- 

 dicular to the plane of incidence. 



It seems of importance to pay attention to the angle 

 between the. intersection of the plane of incidence 

 and the quaternary axis situated in the cubic face 

 of reflection. Fig. 3 shows that when this angle 

 (which was o in Fig. 1) becomes 45°, the curve of 

 spots is deflected, the regularly reflected spot being 

 no longer on the main axis but following the ordinary 

 law of reflection ; the distance of the fringes is prob- 

 ablv slightlv changed in this case. 



I have often observed fringes in the transmitted 

 spots obtained by Laue's methods. With octahedric 

 magnetite (Fig. i) all the spots (more than ioo)_ were 

 striated bv parallel fringes; and on a plate (Fig. 5I 

 obtained with fluorine the transmitted spots, the 

 number of which was also very large, are all doubled 

 in a radial direction. 



