154 ANNUAL OF SCIENTIFIC DISCOVERY. 



that crystal glass is worked at 833°, and becomes completely 

 liquid at 929°. A Bohemian green ghiss tube softens at 769°, and 

 becomes liquid at 1,052° ; pure limestone loses its carbonic acid by 

 heating for several hours at 617°-675°. An increase of tempera- 

 ture will shorten the time. 



METHOD OF CRACKING GLASS. 



Mr. John M. Little, at a meeting of the Massachusetts Insti- 

 tute of Technology, exhibited some novel specimens of curved 

 and tubular glass, cracked by a process which he had devel- 

 oped, showing a great and unexpected elasticity in this substance. 

 After describing the old and unsatisfactory methods familiar to 

 all chemical students, he explained this process, which consists 

 in directing a gas flame, from a glass tube Avith an opening in 

 its point so fine as to cause a needle-like jet, upon a crack pre- 

 viously started by a file. He can then run the crack before the 

 flame in any direction he pleases, except that he cannot run one 

 crack into another, — a fact which he explains by the supposition 

 that an equal portion of the glass is heated on each side of the 

 crack, and that when the line of fracture returns to near its com- 

 mencement it must branch off in order that this necessary space 

 may occur on both sides of its course. He showed that the fibre 

 of the o^lass has nothino^ to do with the direction of the cracks. 

 He can thus crack thick glass, even wine bottles ; in this way 

 utilizing for purposes of the household and the arts many hereto- 

 fore useless broken glass vessels. 



ELECTRICAL THERMOMETER. 



A new English invention is an apparatus for employing elec- 

 tricity, in connection witli a thermometer, to regulate the tempera- 

 ture of a room. An ordinary mercurial thermometer is provided 

 with a platinum wire inserted in a glass bulb, so as to be in con- 

 nection with the mercury. Another wire, capable of elevation or 

 depression, is placed at the other end of the thermometer. These 

 two wires connect with the two poles of a battery, and forming 

 part of the circuit is an electro-magnet, whose armature controls 

 the opening or closing of a valve regulating the admission of hot 

 air. If it is desirable that the temperature of the room should not 

 rise above 60° F., the point of the movable platinum wire is 

 brought to that number on the thermometer. When the mercury 

 registers 60° the circuit is closed, and the armature of the magnet 

 closes the hot-air valve until the temperature becomes reduced, 

 when the valve is again opened. Thus a nearly even temperature 

 may be maintained, — a very desirable object in hot-houses. 



THE FRENCH BAROMETROGRAPII. 



It is usual in takins: barometrical and thermometrical observor 

 tions for the purpose of registration, as regards changes of 



