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POPULAR SCIENCE REVIEW. 
the superstructure, and the Thunderer without it, and suggest certain minor 
alterations in the designs. In regard to the Cyclops class of vessels, they 
are equally satisfied as to their stability, even without a superstructure, 
under any conditions of wind and sea to which they will be likely to be 
exposed in the defence of our coast and in making voyages from port to 
port in favourable weather. They recommend that the four vessels of this 
class in course of construction should be completed with certain minor 
modifications. 
Stability of Ships. — Some advance is made in the theory of the stability of 
ships, which since the disaster to the Captain has assumed so great a prac- 
tical importance, in an interesting paper, read before the Institute of Naval 
Architects, by Mr. W. H. White and Mr. W. John. The paper is too 
mathematical for extract in these notes, but will well repay perusal. 
Machine for Testing Metals. — An extremely interesting machine for test- 
ing metals on a new method has been invented by Mr. G. Bischoff, of Bonn, 
and was described in a paper read before the British Association. It has 
since been exhibited at the Institute of Naval Architects, and illustrated in 
engineering. Mr. Bischoff first prepares small test strips of the metal 
whose quality is to be ascertained. These are 7 mm. and 65 mm. long, 
and are prepared specially by methods which need not here be described. 
The test strips are then placed in a machine called a metallometer, in which 
the test strips are bent backwards and forwards through a definite angle, by 
preference an angle of 67£°. These bendings are effected by a clockwork 
arrangement, and indicating dials are provided to register the number of 
oscillations to which each strip is subjected. Ten strips can, if necessary, be 
tested at one time. The number of bendings which each strip sustains is, on 
Mr. Bischoff’s system, the measure of the quality of the metal, and, according 
to his experiments, would seem to be an exceedingly delicate test. In 
order to have some fixed standard to which to refer the tests of other speci- 
mens, Mr. Bischoff selects strips of chemically pure zinc. The resistance of 
such strips is remarkably uniform. Knowing the average test of say 
50 strips of zinc, in any given machine at any given angle of bending, we 
have a standard with which to compare the results of tests on other mate- 
rials in the same or other machines. So delicate does Mr. Bischoff believe 
his method of testing to be, that he asserts he can by its aid detect the 
deteriorating effect of *00,001 per cent, of tin when alloyed with pure zinc. 
The objection to Mr. Bischoff’s system is that at all events, in certain cases, 
the preparation of the test strips involves processes which alter the mecha- 
nical properties of the material. 
New Form of Braced Bridge. — Professor Pleeming Jenkin has invented a 
new form of braced airch bridge, and has described the mode of determining 
the stresses on the different parts of it, in a paper communicated to the 
Scottish Society of Arts. The stresses are determined by a new graphic 
method of great interest in itself, and which is due to Professor Clerk 
Maxwell. Professor Jenkin’s braced arch is something like an ordinary 
Warren girder, in which the bottom boom, instead of being straight and 
parallel to the top boom, is curved into an arch. In the common bowstring 
girder the depth of the girder is greatest at the centre of the span and least 
at the ends. In Professor Jenkin’s, on the other hand, the depth is greatest 
