430 



NA TURE 



[March 6, 1902 



for the distance between lines or points which can be barely 

 separated. Microscopic test objects are not self-luminous, like 

 double stars, but are viewed by transmitted light. If no con- 

 densing arrangement is employed, the pencil of light sent by a 

 point of the object to the objective consists, in effect, of 

 rays from different sources. The result of this is that the 

 im.ige of the point is larger and more blurred. The cure 

 for this evil is furnished by employing a condenser of high 

 quality, to throw upon the part of the object under examination 

 a very sharp image of the source of illumination. Each point 

 of the object thus gets its light from its own special point of the 

 source ; the object, therefore, acts as if it were self-luminous, 

 and the power of the instrument is increased. The benefit 

 derived from sharp focussing on the object explains the advan- 

 tage of using an achromatic condenser and not, as formerly 

 recommended by Abbe, one which is not achromatic. Another 

 advantage of sharp focussing by the condenser is that there can 

 be no interference of the light from different parts of the object. 

 The author then gives an explanation of the advantage of oblique 

 illumination, and arrives at the view of microscopists that the 

 obliquity of illumination should be rather less than the obliquity 

 of the extreme rays of the incident pencil. The paper concludes 

 with Ilockin's proof of the sine condition. — A paper on the 

 absorption, dispersion and surface colour of selenium, by I'rof. 

 R. W. Wood, was read by the secretary. The dispersion of 

 selenium has been investigated by means of prisms made in the 

 same manner as the cyanine prisms already described by the 

 author. The substance is much more transparent than cyanine, 

 and prism angles of four or five degrees can be employed. 

 Determinations were made with three selected prisms down to 

 wave-length 6i ; below this the interferometer method was 

 employed. Uniform films of selenium were obtained on plates 

 of plane parallel glass Jjy means of a flat selenium kathode in a 

 high vacuum, and the displacements of the interference fringes 

 by the introduction of the films were measured for lights of 

 different known wave-lengths. Wedge-shaped films were then 

 employed, which allowed the displacement for any wave-length 

 to be measured for the maximum thickness capable of trans- 

 mitting the light. An advantage of the wedge-shaped films is that 

 the fringes are curved and the displaced fringe can be easily identi- 

 fied with the undisplaced. The refractive indices obtained in the 

 red by prisms were used as a basis for the calculation of the indices 

 in the rest of the spectrum from the interferometer measure- 

 ments. Determinations were made in this way down to wave- 

 length 40. beyond which it was impossible to go owing to the 

 powerful absorption. A curve has been plotted showing the 

 relation between refractive index and wave-length. It has a 

 maximum at wave-length 50 "00005 cm.), where the re- 

 fractive index is 3 '13. An examination of the light trans- 

 mitted by a thin film showed that there was no return of 

 transparency in the ultra-violet at least down to wave-length 2S. 

 Photometric measurements were made of the transmitted light, 

 both visible and ultra-violet, and a curve has been drawn 

 with wave-lengths as abscissx and extinction coefficients as 

 ordinates. It is proved that the extinction coefficient increases 

 continuously with decrease in wave-length as far as wave-length 

 22, where the coefficient has as high a value as in the case of 

 metals. The author concludes that the absorption is due, not 

 to a single band, but to a series of overl.ipping bands. The 

 object of this work was to determine whether there was a 

 return to partial transparency in the ultra-violet region. This 

 question appears to be answered in the negative, although a 

 possible turning-point in the curve might be masked by the 

 reflection coefficient of selenium. The high value of the ex- 

 tinction coefficient in the ultra-violet led the author to look for 

 traces of selective reflection in this region. The light of an 

 arc lamp was reflected successively from six surfaces of selenium, 

 and the image of the crater after the sixth reflection, although 

 faint, was without colour or excess of ultra-violet light. If the 

 data obtained in the paper for refractive index and extinction 

 are used in the formula for reflection from an absorbing 

 medium, a result is arrived at which indicates that the reflection 

 increases rapidly with decreasing wave-length. As multiple 

 reflections from selenium surfaces give no trace of colour, errors 

 must exist in either the refraction or tlje extinction curve. The 

 author suggests that in the case of films of thickness less than 

 the wave-length of light, the displacement of the interference 

 fringes does not give a measure of the refractive inde.x. — The 

 chairman exhibited some tellurium mirrors made in the same 

 way as the selenium ones used by I'rof. Wood. 



NO. 1688, VOL. 65] 



Chemical Society, February 19. — Prof.Kmerson Reynolds, 

 V. P. R.S., president, in the chair. — The union of hydrogen and 

 oxygen, by Mr. M. B. Baker. The author has devoted, during 

 the last few years, much attention to the inhibition of chemical 

 action produced by thoroughly drying substances, but until quite 

 recently had not succeeded in so completely desiccating a mix- 

 ture of oxygen and hydrogen as to prevent the explosion of such 

 a mixtare when electric sparks were passed through it. He 

 has now found that by electrolysing a solution of barium hydr- 

 oxide it is possible to obtain a mixture of these gases which, 

 when dried over phosphorus pentoxide, is no longer exploded 

 by electric sparks or by the application of intense heat, the 

 highly explosive character of the mixture, however, being re- 

 gained by the introduction of a mere trace of moisture. — Kn- 

 zyme action, by Prof. A. J. Brown. Some years ago the author 

 showed that the fermentation of saccharine solutions by yeast 

 does not proceed according to the ordinary mass law which 

 governs chemical reactions. On the other hand, O'Sullivan and 

 Tompson found that the inversion of cane sugar by the enzyme 

 invertase follows this law. Since both of these reactions, in the 

 light of Buchner's researches on zyma.se, are produced by 

 enzymes, there appeared to be a remarkable difference in the 

 operation of the latter. The inversion of sucrose by invertase 

 has, therefore, been reinvestigated by the author, who finds that 

 this reaction does not progress according to the mass law, but 

 in precisely the same Wiiyas the fermentation of sugars by yeast. 

 The explanation of this feature of enzyme action is, the author 

 thinks, the formation of an intermediate unstable compound 

 between the enzyme and the substance it is decomposing, thus 

 introducing a time factor which obscures the mass influence. — 

 On the velocity of hydrolysis of starch by diastase, with some 

 remarks on enzyme action, by Mr. H. T. Brown, F. R.S. , and 

 Mr. T. A. Glendinning. The authors confirm the results ob- 

 tained by Prof. Adrian Brown with regard to the jirogression of 

 hydrolytic reactions caused by enzymes, but they explain the 

 peculiarity exhibited in a different manner, an attempt being 

 made to connect enzyme hydrolysis with acid hydrolysis, the un- 

 stable combination of starch or sugar with the enzyme being 

 regarded as the hydrolyte and the active dissociated water 

 molecules present as the hydrolysis. — Polymerisation products 

 from diazoacetic ester, by Dr. O. Silberrad. Three series of poly- 

 merides are obtainable from diazoacetic ester, and the present 

 paper gives an account of the results of experiments on the so- 

 called " pseudo-diazoacetamide," whereby the author has been 

 able to assign a constitution to this substance. — Condensation of 

 phenols with esters of unsaturated acids, by Dr. S. Ruhe- 

 mann. The author describes the products obtained by the 

 action of ethyl chlorofumarate on guaiacol and a-naphthol, 

 whereby a benzopyrone and a naphtharone are respectively 

 formed. — The chemical ch.ange produced by the immersion of 

 lead in distilled water, by Dr. F. Clowes. Distilled water, re- 

 cently boiled, exerts very little action upon metallic lead immersed 

 in it, but unboiled distilled water converts the metal into 

 hydroxide of le<ad, which remains in solution, and into a 

 hydrated carbonate, which is precipitated. The principal agent 

 in effecting this change appears to be the oxygen dissolved in the 

 water. — The bases contained in Scottish shale oil, part i. , by 

 Messrs. F. C. Garrett and J. A. Smythe. The fraction of Broxburn 

 shale oil boiling below 164° contains pyridine and several of its 

 homologues. — Note on liquid nitrogen peroxide as a solvent, 

 by Prof. P. F. Frankland, F.R.S., and Dr. R. C. Farmer. The 

 authors note that in their recent paper on this subject they inad- 

 vertently omitted any reference to the previous work by Bruni 

 and Berti, who investigated the cryoscopy of nitrogen peroxide 

 solutions of various substances and pointed out the associating 

 power of this solvent. 



Linnean Society, February 6. — Prof. S. H. Vines, F.R.S., 

 president, in the chair. — Prof. Reynolds Green, F.R.S., ex- 

 hibited some primroses which showed the rare phenomenon of 

 sepalody. The corolla was green and the limbs of the petals 

 were rugose and of a texture almost comparable with that of the 

 foliage-ieaves. He also showed another specimen in which the 

 calyx as well as the corolla was petaloid. Both specimens were 

 received from a garden in the north of Englaml. — Messrs. H. 

 and j. Groves exhibited a series of British hybrid batrachian 

 Ranunculi, together with specimens of their supposed parents. 

 They pointed out that the hybrids were usuall)- characterised by 

 (I ) being intermediate in appearance between the two parents, 

 having some of the distinctive characters of each, but with a 



