NATUBAL PHILOSOPHY. 151 



degrees indoors ; but when exposed to a current of air, even at the 

 same temperature, we feel cold in proportion to the force of the cur- 

 rent, or in proportion to the conducting power imparted to it by in- 

 creased moisture. Both these are agencies of which the thermometer 

 takes no notice. Its indications are furnished by the contractions or 

 expansions of a fluid, whether mercury or 'Spirit, which always main- 

 tains the same temperature as the surrounding medium, and accom- 

 modates itself to these changes by altering its own density in the 

 same proportion. The living animal, on the contrary, as always 

 maintaining a temperature of its own, and as constantly resisting 

 cooling agencies, is not to be considered as passively submitting, like 

 the fluid of the thermometer in its ordinary state. When heated to 

 ninety degrees Fahrenheit, that being nearly the temperature of the 

 surface of our bodies in the rapidity with which it is cooled, de- 

 pending on the intensity of the cooling influences, it furnishes an 

 index to their combined effect. It does not depict the force of any 

 one of the cooling influences taken singly, but gives the sum of them 

 all acting simultaneously." The facts illustrated by the heated ther- 

 mometer are at least six in number, according to the experiments hith- 

 erto performed by Dr. Osborne. It shows the conducting power of air 

 and water ; the cooling effects of currents of air and water ; the effect 

 of wind in cooling the body and all other objects of a higher tempera- 

 ture than itself; the refrigerating effect of air admitted into apart- 

 ments ; the degree of heat derived from fires in rooms as compared 

 with the cooling effect of currents rushing towards the fire ; and the 

 cold and heat of climates as actually felt by human beings. It is 

 evident that a heated thermometer is capable of many useful appli- 

 cations. 



New Barometer. Barometers, of the size of a Geneva watch, and 

 weighing but two and a quarter ounces, have recently been intro- 

 duced. Their accuracy is guaranteed to be fully equal to other 

 instruments in general use, and the price is 4 10s. 



THE PROBABLE CAUSE OF THOSE EXPLOSIONS OF STEAM-BOILEPtS 



CALLED FULMINATING. 



The following is the substance of a paper on the above subject 

 recently presented to the French Academy of Sciences by M. Man- 

 gin : It results from the admirable experiments of M. Dufour, 

 that the temperature of water may, under certain circumstances, be 

 brought to 178 Cent. (352.5 Fan.) without the production of boil- 

 ing. These circumstances are the insulation from contact with the 

 vessel, and insulation from contact with the air. Ebullition is pro- 

 duced by contact with a solid, that is, by the disturbance of the mole- 

 cular equilibrium, and there is then a sudden evolution of steam. 

 Nevertheless, every solid contact is not equally efficient in producing 

 this change of state, and it results from the experiments of M. Duibur 

 that isolation from contact with the vessel is not absolutely necessary 

 for the production of the phenomenon. What appears to be indis- 

 pensable is that the water shall be deprived of air, that the opera! ion 

 shall be carried on slowly, and that the heated mass shall be with- 

 drawn from external disturbing causes. Having explained these pre- 



