118 SUMMARY OF CURRENT RESEARCHES RELATING TO 



from sliding off. The groove along centre of base-plate will enable the 

 operator to remove cover-glasses easily by means of forceps. 



Treadle — Mounting Volvox. English Mechanic, lxxx. (1904), p. 300. 



Villa g io — Mounting Algae. Tom. cit., p. 315. 



(6)2 Miscellaneous. 



Bdhm and Oppel's Microscopical Technique.*— This well-known 

 little volume on microscopical technique contains curt and compressed 

 information for the histological investigation of animal tissues and 

 organs, and its value is increased by a contribution from the late 

 G. Born on reconstruction methods. Though the present issue has 

 been revised and added to by A. Bohm, no reference is made to the 

 Jenner or Romanowsky methods of staining, both procedures being in 

 everyday use and of the greatest value. 



Darwin, H.— Electric Thermostat. 



[An instrument designed and constructed for the special object of main- 

 taining the prism and other parts of the spectrograpli of a 24-inch refractor 

 at a constant temperature, but the principle of the apparatus might be 

 adapted for other kinds of thermostats.] 



tkSL Mag., vii. (1901) pp. 408-14(1 pi.). 

 Hesketh Walker — Notes on marine aquaria. 



English Mechanic, lxxx. (1904) p. 324. 

 Huggins, C. H. — Acetylene as a gas for bacteriological laboratories. 



Centralbl. Baht., l te Abt. Ong., xxxvii. (iy04) pp. 317-20 % 



Kosenau, M. J. — Method for inoculating animals with precise amounts. 



Hyg.-Lab., U.S. Mar.-Hosp. Service Bull. 19, 

 Washington, i904, p. 7 (2 tigs.). 



Metallography, etc.| 



Hardness of Metals.f— At a meeting of the Birmingham Metal- 

 lurgical Society of the Municipal Technical School, Professor Turner 

 gave a lecture on the hardness of metals. The lecturer said that 

 hardness was a property of great importance in connection with the 

 practical application of metals to the arts. In some cases, as with a knife- 

 blade, the continuance of a good cutting edge was of the utmost im- 

 portance ; while in other instances, as with castings which have to be 

 machined, softness was a special requisite. The relatively small differences 

 in hardness which resulted in success or failure were such as could only 

 be measured by accurate methods. Hardness might be defined as the 

 resistance offered by a body to penetration by another body. As the 

 penetrating substance might act in various ways, such as by making a 

 sharp cut, an indentation of considerable size, or an abrading effect, the 

 measure of hardness would depend upon the system of test adopted, and 

 the rapidity with which the test was made. No one test would suit all 

 practical requirements. It was pointed out that in alloys the hardness 

 differed from the mean of the constituents, and was usually higher 

 than that with pure metals. The lecturer then gave a brief historical 

 account of fcue developments of the methods for determining relative 

 hardness. Among the methods specially recommended by the lecturer 



* It. Oldenbourg, Munich and Berlin, 5th ed. (1904) 271 pp. 

 t English Mechanic, lxxx. (1904) p. 404. 



