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Messes. Editors—Mr. Simeon Halton, of his place, an ingenious mechanic, has just )rought out a dial thermometer, in which the ise of liquid of every kind is dispensed with. Fhe instrument is about the size of a common ratch, (which it very much resembles,) only t is not quite so heavy. It is self-register-ng, and may be carried or placed in any rosition without affecting the accuracy of its ndications or the arrangement of its parts, vhich are very firm, and not liable to get out )f place. It is very sensitive, and capable )f indicating with perfect accuracy any de-;ree of heat or cold, showing with the same "acuity the temperature of the boiling-point md that of the poles. The dial may be made )f any desired size, and either of the thermal scales placed thereon. Such are the claims )f its inventor ; and the tests to which it has been subjected thus far fully sustain them. T. H. McLeod. Middlebury, Vt., December, 1857. [We seldom pay attention to notices which ire frequently sent to us respecting new indentions, made here and there throughout the ;ountry, especially when they come merely as commendatory testimonials, without descrip-;ions of the inventions. The above has come to us in this shape, but nothing of the mere puffing style, we are sure, was intended by our correspondent. His letter deserves attention, from the very nature of the subject. If Mr. Halton has invented a solid thermometer which can measure low temperatures equally as well as high temperatures, then he has accomplished a most important object. If not, he has invented nothing new or important, as dial solid thermometers, for measuring high degrees of heat, are old and well known. All bodies expand by heat, and contract with cold. The above mentioned thermometer, we presume, is made of a coiled slip of metal ; but while some solids are better than fluids for measuring high degrees of heat, they are inferior for measuring low degrees, owing to their small amount of contraction at low temperatures. They are also not so good as the usual fluids, mercury and alcohol, for constant common service, because, by very frequent expansions and contractions under heat and cold, the metal soon loses its elasticity, and becomes Incapable of performing its functions aoourately. Solid thermometers oalled pyrometers, have long been empleyod for testing the heat of furnaces, and the melting point of metals. The most improved instrument of this character, we believe, is that of Professor Daniels, of London. The part of it on which the heat acts is a small round platina rod, placed within a tube of baked graphite, and secured by one end to its bottom. To the other end of this rod is attached a fine platina wire, which passes twice round the axis of a wheel, and is fastened to a spring to maintain its tenison. The teeth of the wheel on this axis take into a pinion, on the axis of which is a pointer, the movements of which around a stationary dial indicate the expansion and contraction of the platina rod, and the consequent degrees of heat to which it is exposed. It is a dial solid thermometer. That of Mr. Halton may be different in construction ; but if it can measure very low degrees of temperature as well as mercury, it is certainly superior to the pyrometer of Professor Daniels.—Eds.
