Intelligence and Miscellaneous Articles. 167 



over it was not very long, it could not be broken in the ordinary 

 manner. I made a few experiments in order to ascertain the great- 

 est tension at the time of the fracture. In an oval brass holder 

 small holes were bored, through which the tail was introduced ; the 

 pear-shaped part projected sufficiently, and the part in the holder 

 was fixed by means of gypsum. Two waxed threads fastened to the 

 projecting part formed a small loop, on which, by means of a hook, a 

 scale-pan could be suspended, into which shot fell in a thin stream 

 from a small height. The following measurements were previously 

 made : — the horizontal distance I of the hook from the holder ; the 

 axes a and b of the elliptical section in the neighbourhood of the 

 holder, a being supposed horizontal. The experiment yielded the load 

 Pfor the moment of the fracture. Denoting by R the greatest ten- 

 sion in the external parts of the section for the same moment, we 

 have, by a known principle, 



Pl=R^ab\ R = 3 ^ Z . 

 32 -nab" 



The following Table contains the results of three experiments, 

 where R is given in kilogrammes to the square millimetre : — 



a. b. I. P. R. 



millims. millims. millims. kil. Ml. 



1. . . . 3-20 3-40 24 14 92*5 



2. . . . 3-70 430 38 9"8 55'4 



3. . . . 3-19 3*40 26-2 7*8 56*4 



The values of R thus found are rather uncertain, but of a mag- 

 nitude met with in Tables on the rigidity of metals only in the case 

 of steel and iron. 



Glass vessels containing water in which the pear-shaped part of 

 a tear is held when it is broken off are, as is well known, frequently 

 broken even when the sides are pretty thick. Still more interesting 

 is the following experiment: — A glass tear is held by means of a 

 lateral stand in the middle of a small opodeldoc bottle, and molten 

 resin is poured into the glass. If now after the resin has quite soli- 

 dified and cooled the projecting tail be broken off, the glass smashes 

 with violence ; the fragments of resin which have been in contact 

 with the glass show deep fissures ; but, what is the chief point, 

 the glass tear itself forms a continuous whole, though rather loosely 

 aggregated, which has detached itself like a kernel from the burst 

 resinous shell. The surface of the pear, which of course has become 

 opake, exhibits a peculiar glitter. If the kernel be broken in pieces, 

 a body is readily obtained consisting of a lower hemisphere and su- 

 perposed cone, suggestive of certain forms of hail. 



Parallel to the plane of contact of the cone there appears a tole- 

 rably regular separation in layers in the kernel ; and since the sur- 

 faces of the cracks form in certain places small angles with the 

 surface, the above-mentioned glitter is easily explained. 



I restrict myself to the communication of the above facts. A per- 

 fectly satisfactory explanation of the causes of the hardness and brit- 

 tleness of hardened glass and steel we do not possess, so far as I 



