THERMO ME TERS. 



635 



artificial temperature he was able to produce, or perhaps the lowest natural tem- 

 perature observed by him in Iceland, but recently a novel explanation has been 

 published by an anonymous writer in the Ohio State Journal, which is described 

 and illustrated as follows : 



Fahrenheit was a mathematician and knew that a circle was divided into 

 360°. He found that steam and ice were the most natural fixed points in tem- 

 perature, at opposite poles. He therefore naturally divided the distance on his 

 glass tube between ice and steam into the number of degrees in the diameter of a 

 circle, which is 180°. He wanted an instrument which could be cheaply made 

 and which would measure above steam and below ice, so far as would be com- 

 monly used in everyday life. He found that artificial cold could be produced 

 which would cause the mercury to fall just thirty- two of the spaces he had marked 

 off on his glass between ice and steam, and he there, whether sensibly or not, 

 placed his zero or point from which he would count. Hence ice, or freezing, is 

 32° above, and steam or boiling water is the diameter of his circle, or 180° above 

 ice, or 212° above zero. This may appear very novel and ingenious, but its utter 

 absurity is apparent when we remember that the diameter of a circle is not 180°. 

 We only refer to it here because we have seen it prominently copied in respecta- 

 and influential newspapers. 



In converting degrees of one therraometric scale into those of another the 

 following formulae may be used : 



Centigrade Degrees-i-sXP "H 



32=Fahrenheit Degrees. 

 32= 



=Centigrade 



=Reaumur 



Reaumur *' -4-4X9 " 



Fahrenheit " — 32-T-9X5 



" -32--9X4 



Centigrade " -4-5 X4 = " 



Reaumur " -4-4 XS =Centi grade 



Mercury expands quite regularly between — 36° and 2 1 2 ° F. Above 212° the 

 expansion is less regular and the indications less exact. As mercury boils at 

 660° F., the hmit of the scale in this direction is sufficient, but since it freezes at 

 — 38° F., alcoholic thermometers must be used for lower temperatures, for this 

 liquid has never been frozen. 



Thermometers for maximum and minimum temperatures have been invented 

 by several persons. They are self-registering, and this is effected by a small 

 index within the tube which moves with the mercury in one direction and not in, 

 the other. 



