

Notices respecting New Books. 55 



soft gray cast Iron: metal of this kind yields easily to the File, 

 when the external crust is removed, and is slightly malleable 

 in a cold state." 



Section VI, Arts. 68 b to 68 ', contains Experiments on 

 malleable Iron, English and Swedish, on Steel, on Gun- 

 metal or Bronze, and on Brass : wherein, as to Iron, the ef- 

 fect of hammering and the decrease of force by heat, are ex- 

 perimentally examined, and the cause of English Iron being 

 inferior to Swedish, for particular purposes, is pointed out. 

 The novel and important object which Mr. Tredgold has had 

 in view in all his Experiments, has been, to ascertain the 

 exact strain that Materials would bear, and with what flexure, 

 without impairing their elasticity, so that on removing the 

 strain, this might cause them to recover perfectly, the flexure 

 which the strain had occasioned ; whereas almost all previous 

 Experiments were carried, from 3 to 4 times as far, as to 

 strain, in order to observe, the almost useless point, at which 

 actual breaking took place. 



In Section VII, and the others which follow, wherever 

 Fluxions have been used by other Writers, in the investiga- 

 tion of the general Formulae, the Author has instead, had 

 recourse to the method of progression, which he first de- 

 scribed in 1821, in three papers in our 57th volume. In Art. 

 121 a is now given, a Table of the Thickness, Breadth, and 

 Pitch of the Teeth of Wheels, followed by ample directions 

 and examples of its use ; and it is ascertained, that the pro- 

 portions here theoretically assigned, agree very nearly with 

 those, long in use by the most esteemed of our makers of 

 Machinery in the large way. 



In Art. 139 a is now inserted a Table of the proportions of 

 Gudgeons or Pivots, for different degrees of strain or stress : the 

 diameters of the gudgeons in this Table, are from \ to 10 inches, 

 their lengths - 43 to 85 inches, and strain from 213 to 85,000 lbs. 

 In Art. 156 a the addition is made, of a Table of Cast Iron 

 Joists for Fire-proof Floors, when, besides the flat Brick Arches, 

 the extraneous Load is not to be greater than 120 lbs. on the 

 superficial Foot : At the conclusion of the directions for using 

 this Table, the Author observes " The construction of these 

 Floors, renders a place secure from Fire, without loss of space, 

 and with very little extra expense : it may be of infinite use 

 in the preservation of Deeds, Libraries, and indeed of every 

 other species of property. In a public Museum, devoted to 

 the collection and preservation of the scattered fragments of 

 literature and art, it is extremely desirable that they should 

 be guarded against Fire: otherwise, they may be involved in 



one 



