April 25, iHg^] 



NATURE 



611 



zVa for five wave-lengths, obtained from the measure- 

 ments of the apparent acute and obtuse angles in mono- 

 bromnaphthalene by the use of accurately orientated 

 section-plates, are so close together that it was con- 

 sidered advisable to ascertain in some other manner 

 whether the order of dispersion was truly represented ; 

 that is, whether the angle for one end of the spectrum 

 was really very slightly greater than that for the other 

 end, or whether the amount of dispersion thus indicated 

 did not really fall within the limits of experimental 

 error, thus leaving it possible that the dispersion might 

 even be of the contrary order. By immersing a plate 

 perpendicular to the first median line in a liquid of re- 

 fractive power equal to the medium refractive index of 

 the crystal, the interference figure in white light usually 

 at once indicates, by the colours exhibited on the margins 

 of the axial brushes, the order of dispersion, and measure- 

 ments of the axial angle for the two extreme wave- 

 lengths afford an immediate check upon the accuracy of 

 the calculated angles. It is a considerable source of 

 satisfaction to be able to confirm such calculated optic 

 axial angles in so simple a manner. 



Prof Klein further describes how admirably the new 

 apparatus is adapted for the determination of the ex- 

 tinction angles upon the various faces of a zone, in 

 parallel polarised light. For this purpose the converging 

 lenses are removed, and the eyepiece analysing nicol is 

 employed, so that the polarising and analysing nicols 

 may be arranged for simultaneous rotation. The mea- 

 surements are earned out while the crystal is immersed in 

 the liquid as in case of the determinations of optic axial 

 angle. The only precaution necessary is that the crystal 

 should be uniformly illuminated in order that the exact 

 position of extinction may be ascertained by use of one 

 of the usual half-shadow stauroscopic plates. 



The memoir concludes with a description of the general 

 mode of investigating a biaxial crystal immersed in a 

 liquid of equal refractive power, indicating how the 

 principal planes of optical elasticity may be found, the 

 positions of the optic axes ascertained, and the true 

 internal angle of the latter measured. One of the most 

 important advantages of the method is the simplification 

 which it introduces into the study of triclinic crystals, 

 hitherto almost dreaded by the crystallographer for the 

 trouble they involve. It would appear that their optical 

 investigation by the immersion method otters but slightly 

 more aitticulty than that of crystals of higher symmetry, 

 the positions of the optic axes being readily found, and 

 the true angle at once i.iTorded. This alone would 

 entitle Prof. Klein to the thanks of crystallographers and 

 mineralogists for perfecting so admirable an aid to 

 investigation. A. E. TUTTON. 



MICROBES AND METALS. 



'T'HE effect of metals on the growth of bacteria has 

 ■*■ been examined by Miller, Behring, and others, and 

 another contribution to this subject has lately been pub- 

 lished by Ur. Meade Bolton, in the December number of 

 the International Medical Magazine. According to 

 Uffelmann, who smeared the surface of copper coins 

 with liquefied jelly-cultures of cholera bacilli, the latter 

 were destroyed in seventeen minutes ; whilst on a brass 

 coin they were alive after thirty hours, but dead after 

 sixty hours. Bolton employed Miller's method of in- 

 oculating a tube of melted jelly with particular microbes, 

 and pouring the contents out on a sterilised glass-plate, 

 after which bits of the metal under examination were laid 

 on the jelly whilst it was still soft. If the metal has an 

 inhibitory action on the microbes, then a clear zone is 

 left around the metal after the colonies have developed 

 in the other parts of the jelly. The width of this zone. 

 Dr. Bolton found, varied very considerably with different 



NO. 1330, VOL. 51] 



organisms, as well as with different metals. Thus care- 

 fully purified bits of silver produced in the case of cholera 

 bacilli a clear zone 5 millimetres broad, in the case of 

 typhoid bacilli a zone of about i millimetre, whilst with 

 the closely allied colon bacillus a zone of about 5 milli- 

 metres was produced. In the case of purified gold, 

 no inhibition was observed with the staphylococcus 

 pyogenes aureus, colon bacillus, typhoid bacillus, or 

 cholera bacillus. Freshly " glowed gold" had invariably 

 no inhibitory action ; and in the few cases where inhibition 

 was observed, the gold had not been glowed for several 

 weeks. Pure nickel, platinum wire, and platinum black 

 aluminium, silicon, and niobium, again, also failed to 

 give any reaction with most of the microbes examined. 

 Throughout the investigations it was found that those 

 metals that are resistant towards chemical reagents in 

 general, failed to produce any effect on microbes ; 

 whilst, on the other hand, those metals which are readily 

 attacked by chemical reagents, all exhibited a marked 

 inhibitory action upon the growth of bacteria. This 

 result is probably due to a solution of the metal taking 

 place in the medium. The length of time it is necessary 

 to leave the metals in contact with the jelly, to produce 

 an effect on the microbes present, was tried ^vitli brass, 

 copper, cadmium, and zinc, on the staphylococcus 

 pyogenes aureus. The metals were put on and removed 

 at various intervals. When cadmium was left on for a 

 minute, there was a clear space underneath where it had 

 rested, which extended to I millimetre round ; when it was 

 left on for three or four minutes, the clear space usually 

 extended over 3 millimetres. Very similar results were 

 obtained with zinc. With brass no effect was produced 

 when it was left on thirty-six minutes, but after this there 

 was more and more marked inhibition up to fifty 

 minutes ; but to produce a clear space, it was necessary 

 to leave it on for still longer. Copper produced no 

 visible effect under thirty-six minutes, and fifty minutes 

 was required to produce a clear space. 



G. C. Frank L.A.XD. 



PROFESSOR JAMES DWIGHT DANA. 



BY the sudden death of Prof. J. D. Dana, from heart- 

 failure, on April 15, .America has lost a veteran man 

 of science, who in his time has not only played many 

 widely varied parts, but has reached the highest excel- 

 lence in each. .Vs a mineralogist he published, solong ago 

 as 1S37, the first edition of a " Descriptive Mineralogy," 

 which by reason of its completeness and accuracy soon 

 became a standard work of reference throughout the 

 civilised world, and of which the sixth edition (113+ 

 pages), issued in 1S92 under the superintendence of his 

 distinguished son. Prof. Edward Salisbury Dana, still 

 maintains the high reputation attained by the original 

 work. As a geologist and paleontologist, he published 

 in iS63a similarly excellent and well-illustrated " .Manual 

 of Geology," having special regard to the geology of the 

 North American continent, and of which the fourth 

 edition (10S7 pages) was issued only two or three months 

 ago. Of his work as a zoologist, we may cite as example 

 his elaborate report on the zoophytes, collected by an 

 expedition in which he took a very active part. The 

 report is illustrated by 61 plates, and in it are described 

 no fewer than 230 new species. Attainments so diverse 

 belong only to the few. 



James Dwight Dana was born on February 12, 1813, 

 at I'tica, in the State of New York, U.S.A.. and was 

 therefore in his eighty-third year at the time of his death. 

 He was educated at Yale College, New Haven, Con- 

 necticut, receiving there a sound training in mathematics, 

 physics and chemistry, which was of the greatest service 

 to him in his subsequent career ; he proceeded to his 



