412 Progress in Science. (July, 
Glass articles in ordinary use are subject to sudden sharp blows, either from 
falling down, or from some extraneous substance being brought smartly in 
contact with them. Under these conditions the elasticity of toughened glass 
is called into play, and enables it to sustain a shock immeasurably beyond 
that which would suffice to destroy ordinary glass, as is shown by the experi- 
ments first described. Hence the proper tests for glass, either toughened or 
plain, are precisely those of smart and sudden impact, and not of prolonged 
stress. Examination and experiment with this remarkable substance have 
revealed a number of most interesting facts with regard to its physical 
character. The limits of a paper, however, forbid me entering upon these 
considerations at such length as I could wish, and as the subje& deserves. 
I may, however, mention that the microscope reveals the fact that the fractures 
follow a regular order, which gives a uniform shape to the crystals which they 
produce. Large crystals can be subdivided into several smaller ones with a 
similar result. The edges of the atoms, too, are not jagged and serrated, as 
are those of ordinary glass, hence their diminished tendency to cause incised 
wounds, as already mentioned. This peculiarity would afford a means of 
ascertaining whether the glass had been tempered or not. The physical 
character of toughened glass has been made the subject of careful investi- 
gation by M. Victor de Luynes, who made the results of his researches the 
subject of a lecture, which he delivered at the annual meeting of the Société 
de Secours des Amis des Sciences. I hoped to have embodied in my paper 
some of the results obtained by M. de Luynes, but, unfortunately, the rules 
of the Société do not permit the publication of lectures until they have 
passed the examination of a committee, which process M. de Luynes’ paper 
is only now undergoing. I may, however, mention that M. de Luynes had 
a furnace and bath in the le@ure-room, and before his audience he tempered 
glass objects, which were afterwards successfully tested. Asa general result, 
M. de Luynes has found that toughened glass will bear from 80 to roo times 
the strain of ordinary glass. M.de Luynes also examined both plain and 
toughened glass by the aid of polarised light, the results of his examination 
going to show that toughened glass owed its peculiar charateristics to a 
condition of intensified compression. I have explained what toughened glass 
is, how it is produced, and what are its leading features, so far as at present 
ascertained. It therefore only remains for me to indicate the direction of its 
practical application. I say ‘‘indicate,’’ for were I to enumerate all the 
purposes to which it can be usefully applied I should simply become weari- 
some. It is possible that there is not one corner in the whole domain of 
the arts, sciences, and manufactures, where its presence will not in time 
be made manifest in some way or other, and its usefulness appreciated, whilst 
for purposes pertaining to social life its application would seem to be 
unlimited. The miner would have a safer safety lamp than even Davy gave 
him, and the engineer’s gauge glass would stand the highest steam pressure 
and alternations of heat and cold without fear of mischance. In chemical 
works it would supersede lead for tanks, and the present costly and unreliable 
glass pump-tubes would be far less expensive, and infinitely more durable. So 
with brewers; they would find it a most useful friend in their vats, which they 
could thoroughly and easily cleanse, and keep free from those secreted stale germs 
of organic life which develop and reproduce themselves in the process of fer- 
menting beer, in a highly objectionable manner. For water-pipes it would 
offer the advantages of strength, without corrosion. Assayers, I am told, 
would use it instead of platinum in some processes. In silk-spinning 
machinery, slider-eyes, or guides, which are so soon cut through by reason of 
the speed at which the silk passes through them, would be rendered very 
durable if made of toughened glass. Another application, which has suggested 
itself to an ingenious American gentleman since the first notice of M. de la 
Bastie’s invention appeared, is the manufacture of printing-types, and rollers 
for printing-presses, and this idea is now being developed into practical form. 
Seeing the wide range of domestic and social wants which toughened glass 
promises to meet, I know not where to begin, and were I to begin I should not 
know where to end. I can only observe in this connection that toughened 
