280 THE AMERICAN MONTHLY [Sep 



of the micrometer screw projects through a small aper- 

 ture in the plate and is manipulated by a detachable key 

 kept by an attendant. The upper end of the microscope 

 body is provided with a clamping ring which fixes the tube 

 immovably in place. The ocular is likewise fastened by 

 a set-screw. All joints and openings are sealed with felt 

 in such manner as to be dust-proof. The instruments are 

 fitted with ocular II, and objective 3, giving a magnifi- 

 cation of 70, but this combination may be changed from 

 time to time. 



The instruments are fastened in pairs to tables of spe- 

 cial design, and placed in the west hall of the systematic 

 museum. The objects placed under observation aid in the 

 illustration of exhibits in the cases. Suitable explana- 

 tions are given by labels placed on the tables at the side 

 of the instrument. The tables are furnished with heavy 

 iron sills to secure stability, and hold the instruments at 

 a height above the floor convenient for the use of the ma- 

 jority of observers. 



The entire demonstration will form a most attractive 

 and useful exhibit, and it gives the casual visitor the op- 

 portunity of seeing something of the intimate structure 

 of plants. — D. T. McDougal, in Journal of New York Bot. 

 Garden. 



On the Metallography of Iron and Steel. 



WILLIAM H. MERRETT. 



It is well known that specimens of both iron and steel, 

 produced under apparently the same conditions, often dis- 

 play totally different properties. This is especially the 

 case with steel, which, on account of its more complex 

 character, is easily affected by small alterations in the 

 conditions of its manufacture. The causes of the varia- 

 tion in properties of similarly-produced samples of metal 

 may often be explained by the aid of the microscope, when 

 all other methods of investigation have failed. 



