ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 513 



To give a good idea of the size of the plates, I would refer to 

 what is seen in a longitudinal section of medium steel forged from an 

 ingot 3 in. in diameter down to a bar 1 in. square. When broken it 

 shows a very fine graio, and when a prepared section is examined 

 with a moderate power this grain is seen to be due to crystals often 

 about 1/1000 in. in diameter, which are not drawn out or distorted, 

 as they would have been if they had existed previously to final 

 cooling after hammering, and as they are distorted if the steel be 

 hammered at a lower temperature. Examined with a power of 

 650 linear, these crystals only 1/1000 in. diameter are seen to contain 

 something like sixty of the alternating plates, and even this extremely 

 delicate structure shows little or no trace of distortion. Of course it 

 is impossible to separate and analyse such thin plates, and we must 

 rely on induction to furnish us with a knowledge of their nature .... 



It will thus be seen that the use of very high magnifying powers 

 opens out a wide field for research, and has already placed a number 

 of important questions in a new light. As far as I am able to judge, 

 all the facts seen in the various kinds of iron and steel hitherto 

 examined may be explained in accordance with the views here de- 

 scribed ; but the time spent in studying the fundamental questions 

 prevented me from finishing a comprehensive illustrated memoir which 

 was already in large part written before using very high powers." 



TJse of the Microscope with Convergent Polarized Light.* — Dr. 

 A. Wichmann considers that the methods proposed some years ago, 

 almost at the same time by Bertrand, Klein, and Lasaulx, for con- 

 verting the Microscope into a polarizing instrument for convergent 

 light, in spite of their utility in the microscopic analysis of rocks, 

 have not as yet fully answered the expectations which were formed 

 of them. The obstacle to their success is the want of intensity in 

 the interference figures when the sections are very thin, which makes 

 it difficult to observe them with certainty. Where, however, this 

 objection does not apply, the method, as is shown by a paper by 

 Herr F. Becke, gives good results.f 



Experiments with the Electric Incandescent and Arc Lights.J — 

 Dr. M. Flesch has made experiments with the arc light of a Duboscq 

 lamp, with two Edison incandescent lamps of 16 and 8 candle 

 power respectively, and a Swan lamp of 2^ candle power. Tests were 

 applied for the discrimination of colours, and for resolving power by 

 the electric light as compared with daylight. For colour was used 

 a histological preparation injected with Berlin blue, and stained 

 with carmine and iodine green ; for resolution the test - objects 

 employed were Surirella gemma and Nitzschia sigmcidea of Moller's 

 test-slides. The arc light was used at a distance of 1 metre, and the 

 incandescent lamps at a distance of 30-40 cm. from the mirror ; the 

 same results were obtained from both, namely, very good distinction 

 of colours, considerably better than by daylight, and improved resolv- 



* Zeitschr. f. Wiss. Mikr., i. (1884) p. 139. 



t Tschermak's Mineralog. und Petrogr. Mitth., v. (1883) p. 527. 



I Zeitschr. f. Wiss. Mikr., i. (1884) pp. 561-3. 



