466 Intelligence and Miscellaneous Articles. 



gether, are displaced along the same directions and produce the 

 disaggregation of the system. 



If this supposition is correct, one might make a drop burst by 

 cutting it at the large end, in such a manner as to set free at one 

 of their extremities the unequally chilled layers of glass. This is, 

 in fact, what takes place when the large end of the drop is ground 

 off in a lathe, or when we attempt to saw it ; the explosion always 

 takes place as soon as a little more than half of the thickness 

 has been attacked. 



Another consequence of this hypothesis is, that the vitreous 

 molecules will be displaced in a direction different according to the 

 manner in which rupture takes place. This displacement should be 

 greater for the exterior than for the interior layers, which are less 

 expanded ; and it is almost nil for the central portions, which have 

 not been chilled at all or but very little. Consequently, on consi- 

 dering the molecules in a plane transverse section of the drop, the 

 eccentric molecules, belonging to the more expanded layers, will be 

 more displaced than those situated nearer to the centre, which will 

 be less and less so as they are further from the surface ; so that 

 after the rupture this plane section will have the appearance of a 

 conic surface formed of little needles of glass,' arising from the 

 shrinkage on all sides ; and the direction of the summits of these 

 sorts of cones will indicate that in which the displacement of the 

 molecules has taken place. 



if the thin end be broken off, the shrinking will be towards the 

 bulb, and all the summits of the cones will be directed towards the 

 thin end. If the explosion be caused by sawing the big end of 

 the drop, the cones will have their summits directed towards the 

 big end. 



That this is what in fact happens I have ascertained by operating 

 in the following manner. I fit some Rupert's drops in plaster, 

 covering only a little more than half of their thickness. The thin 

 end, which is left protruding, I immerse in nuorhydric acid. The 

 moment the neck is attacked the drop is disaggregated, with or 

 without explosion ; and the fragments constitute, by their grouping, 

 a series of conic assemblages encased one within another and hav- 

 ing their summits towards the thin end. On sawing the big end, 

 the summits have the opposite direction ; and if the drop is sawn in 

 the middle, the two opposite arrangements are observed on the two 

 sides of the incision. Operating while the plaster is fresh, we can 

 easily detach the fragments of the drop and establish all the results 

 I have stated. 



These facts demonstrate that in the drop the glass is in no pecu- 

 liar condition other than that which arises from the unequal expan- 

 sion resulting from the difference of cooling. 



Analogous phenomena are presented by thick glass rods which 

 are chilled naturally by cooling in the air at the moment of their 

 fabrication. When these rods (which have always some curvature) 

 are heated at one end, it sometimes happens that they break along 



