ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 511 



portional to the number of refracting surfaces. The objection that 

 there is also a corresponding loss of light, although practically true, 

 is of no consequence whatever, as is sufficiently demonstrated by the 

 extensive experience in the use of this class of objectives. 



" Summing up, we come to the conclusion that the future high- 

 power objectives will be the four-system water-immersion. Or, the 

 immersion will be done away with altogether as an incurable incon- 

 venience, and the four-system dry- working objective will be used." 



Has not Mr. Gundlach heard of such an important property of 

 objectives as aperture, and does he not know that the limit of 

 aperture of a "dry-working objective" is I'O N.A., while a homo- 

 geneous-immersion objective may approach 1 • 52 N.A. ? 



The microscopist of the future who " does away with immersion 

 altogether as an incurable inconvenience" must, to be consistent, 

 refuse to ride by railway or to send or receive communications by 

 telegraph or telephone. He will probably not carry his consistency 

 so far as to insist upon walking the streets in a state of nature and 

 without the " incurable inconvenience " of clothing, only because he 

 will have just sense enough left to appreciate the fact that his so 

 doing would land him in a prison or an asylum — in the latter he 

 ought at least to be. 



Application of Very High Powers to the Study of the Micro- 

 scopical Structure of Steel.* — Dr. H. C. Sorby writes as follows : — 



" Though I had studied the microscopical structure of ii-on and 

 steel for many years, it was not until last autumn that I employed 

 what may be called ' high powers.' This was partly because I did 

 not see how this could be satisfactorily done, and partly because it 

 seemed to me unnecessary. I had found that in almost every case a 

 power of 50 linear showed on a smaller scale as much as one of 200, 

 and this led me to conclude that I had seen the ultimate structure. 

 Now that the result is known it is easy to see that my reasoning was 

 false, since a power of 650 linear enables us to see a structure of an 

 almost entirely new order, and of such a character that, if it had 

 been on a scale of a quarter or a half the actual magnitude, it would 

 probably never have been recognized, on account of being beyond the 

 resolving power of the Microscope for fine parallel lines. . . . With 

 this arrangement [the Vertical Illuminator] high powers give as good, 

 or even better, illumination than low. Speaking generally, a power 

 of 650 linear is about ten times that previously employed, which is, 

 of course, enough to open out a new field for research. 



This great increase has, however, shown little or nothing more in 

 the case of malleable iron containing little or no carbon, or in the 

 case of the intensely hard constituent of Spiegel iron, of white refined 

 iron, and of blister steel. It has also shown but little more in the 

 case of inclosed slags, or of the graphite in cast iron ; but it has 

 enabled me to see to great perfection crystals which are probably 

 silicon, and has thrown a flood of light on the nature and character 



* Paper read at the Iron and Steel Institute on May 14, 1886. Cf. the 

 Ironmonger, 1886, p. 1)0.5. 



