92 ANNUAL OF SCIENTIFIC DISCOVERY. 



stuffai the pattern must be continuous ; whereas in M. Kuhlmann's 

 plates the lines at one end would clearly not coincide with those at 

 the other, so that disagreeable interruptions would be caused in the 

 printed designs. This obstacle, however, has been overcome in a 

 most ingenious manner by eifecting the crystallization on the 

 cylindrical surface of a roller. A slight rotary motion imparted 

 to it will prevent the liquid from accumulating at any particular 

 point before it has evaporated. 



MICA SPECTACLE-GLASSES. 



As made on the recommendation of Dr. Cohn, of Breslau, the 

 mica spectacle-glasses are curved somewhat in the shape of 

 watch-glasses ; they not only protect the eye in front, but their 

 brass frames fit closely on the osseous circle round the eye-sockets, 

 so that no chips can enter the eye from any part, and still the eye- 

 lashes do not touch the glasses. The frame is made of thin brass 

 wire, which can easily be bent by hand into any shape. As hinge- 

 joints would have caused too much expense, the side parts are 

 soldered on to the frame. The thickness of the mica is about one- 

 twenty-fifth of an inch. Only the purest kind of mica being used 

 for this purpose, these spectacles are just as transparent as real 

 glass ones. They impart, to be sure, a slight pale gray tint to the 

 objects, but they do not in the least weaken the optic nerve of the 

 eye. For blacksmiths and foundrymen such a gray tint is rather 

 an improvement, and for other metal workers it is not in the least 

 objectionable. Now, these mica' spectacles, besides protecting the 

 whole eye, have the following advantages: First, they cannot be 

 broken ; heavy blows with a sledge-hammer only squeeze them 

 flat, without breaking the glasses. They may be thrown to the 

 ground with full force without being damaged in the least. Red- 

 hot metal poured on the mica does not make any impression on it. 

 The shower of pointed particles of iron which issues from lathes, 

 etc., only rebounds from the perfectly elastic mica glasses. Sec- 

 ondly, mica spectacles are almost twice as light as glass spec- 

 tacles ; a pair of French watch-glass-shaped spectacles weighs 13.9 

 grammes; mica spectacles only 7.5 grammes. Thirdly, mica 

 spectacles keep the eyes of the workman cool, mica being a very 

 bad conductor of heat. Fourthly, mica spectacles are very much 

 cheaper than glass spectacles, esiDCcially watch-glass spectacles, 

 which are the only ones that protect the whole eye. The mica 

 spectacles are sold at Breslau for about eight pence, English 

 money, apiece. They would be, of course, a few pence dearer 

 in this countrj^ as carriage, duty, commission, etc., would add to 

 the expense. But, at all events, their cost would be exceedingly 

 trifling when compared with the very serious exi^ense, loss of 

 time, and pain, that are caused to iron-workers by the frequent 

 accidents to their eyes. No doubt there will soon be estab- 

 lished an agency for the sale of mica spectacles in this country, 

 and we shall then hear more about them. As it is, we strongly 



