820 SUMMARY OF CURRENT RESEARCHES RELATING TO 



A little adjustmeut of tlic light was required to get it well through 

 both polarizer and analyser, but this with a little care was soon dune, 

 aud a bright pictuie, several feet in diameter, was ])rojeetcd upon the 

 screen, showing the crystals well defined and exhibiting very strikingly 

 the changes of ctdour, &c., characteristic of the crystals when viewed 

 bv jiolarized light, and in such a manner as to bo well seen by a number 

 of peojde at once and also allowing the lecturer to readily point out any 

 particular crystal or crystals to which he desires to draw the attention 

 of his audience. As the optical axis of the lantern and Microscope did 

 not coincide, the lantern was placed on a board provided with four 

 levelling screws, with which the necessary adjustments were readily made. 



Much bettt^ r effects may be got if the ' Pruzmowski ' form of prisms 

 made by Zeiss are used instead of the usual Nicol's prism on account of 

 their greater aperture and shorter length, and the most brilliant results 

 with the 1 in. objective of fifty angular apertures (sic) by Wray of London."' 



Microscopy and the Study of Rocks.* — Prof. J. W. Judd thinks 

 there is perhaps just now a danger of our exaggerating the importance 

 of the microscopic method as applied to the study of rocks. That the 

 method has already done much in enabling us to follow out and trace 

 the effects of the slow processes of change within the earth's crust, and 

 that it will do still more in the future no one can doulit. But when it 

 is sought to make the Microscope a " court of final appeal " in geological 

 questions, and in doing so to disregard the importance of field observa- 

 tion, we perceive the same source of danger as is now perhaps being 

 experienced in connection with almost every branch of natural history 

 research. It must be remembered that while the Microscope enables us 

 to see a little more than the naked eye or the pocket lens, yet, neverthe- 

 less, between what is actually seen by the very highest powers of our 

 Microscopes and the molecular groupings and reactions which give rise 

 to tlie varied phenomena of the mineral kingdom, there is room f r 

 almost infinite possibilities. We accept the teaching of the Micro- 

 scoi)e with all thankfulness, but we recognize the fact at the same time 

 that it has enabled us to get only a very little nearer to the heart of 

 those great physical problems which we aim at solving. 



Microscope and Telescope.f — M. J. C. Houzeau, formerly Director 

 of the Brussels Observatory, has a lengthy paper under this title, from 

 which we extract the following : — 



" The field of scientific research was immensely widened by the simul- 

 taneous invention of the Microscope and Telescope. In the whole course 

 of history there is not another invention which has exerted a similar 

 influence in the sphere of material facts. The circle of individual action 

 was extended in an unexpected degree by gunpowder ; it was this which 

 enabled Cortez and his four hundred followers to put to flight armies 

 •which outnumbered his own in the proportion of 100 to 1. In the 

 strictly material order of things, gunjiowder is the first signal triumph 

 of applied science — of modern science. But we must grant that it had 

 an essentially destructive character ; it belonged to the arts of war, 

 which in our social childhood take precedence of the arts of peace. 



The second invention which — still in the material world — produced 

 a profound revolution, belonged to the useful arts. This was the steam 

 engine, by which our industrial forces have been enlarged to an enor- 



" Mature, xxxviii. (1888) p. 386. 



t Bull. Soc. Belg. Micr., xiii. (1887) pp. 90-110. 



