Each degree of Reaumur is equal to 2i of one of Fahrenheit. Multiply the given number of degrees of Reaumur by 9, and divide the product by 4. If the degrees of Reaumur were minus, the quotient must be deducted from 32, and the remainder will be the equivalent degrees of Fahrenheit. If the given degrees were not minus, the quotient must be added to 32 degrees, and the sum will be the equivalent sought.
Each degree of Fahrenheit is equal to 1 of one of the centigrade. Proceed as in the case of Fahrenheit and Reaumur, multiplying, however, by 5, and dividing by 9.
Each degree of Reaumur is equal to If of the centigrade. Multiply the given number of degrees by 5, divide the product by 4, and the quotient will be the equivalent number of degrees on the centigrade scale.
Each degree of the centigrade scale is equal to four-fifths of Reaumnr. Multiply the given number of degrees of the centigrade by 4, and divide the product by5; the quotient will be the equivalent number of degrees on Reaumur's scale.
The different degrees of expansibility of dissimilar metals by the same increase of temperature, is well known, and has been usefully employed to produce compensation in the regulators of time-keepers ; and recently a very sensible and convenient thermometer has been made on the same prinoipiw The one from which we made the diagram on the next page, is contained in a common-sized pocket-watch, and indicates the temperature from 30' below zero to 800 Reaumur, equal to the extent from zero, to 2l20 on Fahrenheit's scale.
It consists of a slip of steel on a slip of brass attached together, and bent With the brass inwards, into a circular form a a, and fixed to the frame of the - watch at b, immediately behind the dial. One end of this circular piece is bent inwards at e, and acts upon a lever, a f, of the third order. The lever moves upon a pivot at f, is furnished with an adjusting screw d, and a toothed segment e. The teeth of this segment act upon the teeth of a small pinion g, to the projecting pivot of which an index A is attached.
The action of this little instrument is obvious; for as the interior portion of the compound circular piece is of brass, which is more expansible than the exterior, which is of steel, an increase of heat will cause the ring to open ; but in opening it acts upon the lever, and by that means turns the index, which points out by the graduated circle on the face of the watch the quantity of increase. On the contrary, when a decrease of heat takes place, the ring will
have a tendency to close, and the lever being kept up to it by a small spring on the opposite side, acts upon the index, and points the quantity of decrease in the temperature. This thermometer indicates a change of temperature much quicker than the common mercurial thermometer, owing to the metals being better conductors of caloric, than wood or glass, the substances of which they are usually manufactured.
A. Thermometer of Contact has lately been invented by M. Fourrier. "It is well known," says M. Fourrier, " that on touching different substances maintained at the same temperature, the same calorific impression is not received in consequence of the different conductibility of those bodies. It is even sufficienz to cover those bodies with a thin sheet of paper, sensibly to change the effect or the .contact. If, then, on a support kept at a constant temperature, for example, at that of melting ice, thin sheets of different substances are successively applied, the simple contact of the naked hand will suffice to class a great number of them according to their order of conductibility ; but this method is by no means accurate, and is liable to other inconveniences. M. Fourrier's instrument may be considered as an improved hand, and minutely establishes the facts to which the application of the hand only makes an approximation. It is extremely simple ; it consists of a cone of very thin iron, filled with mercury, and terminated at its circular base by a skin of moderate thickness. A thermometer is placed in the mercury ; it is this skin which is put on the thin sheet applied to the support. The contact is very intimate, in consequence of its flexibility ; and the thermometer indicates the variations of temperature. By this instrument many curious facts have already been ascertained. For instance, it has been shown, that the order in which thin sheets of different substances are placed one upon another, influences the quantity of heat which passes through them under the same external circumstances. Thus, the interposition of a sheet of leather facilitates the transmission of heat from skin to cloth, and it obstructs it from cloth to marble.