Mr Tregaskis on the Expansion of Vapour. 71 



One practical advantage to be derived from the calculation 

 of force by temperature is the application of a thermometer 

 as a check on the safety valves of steam-engines. Many per- 

 sons, not naturally timid, are unwilling to venture on board a 

 steam-vessel through fear of its blowing up. 



A naval officer, distinguished for bravery, told me not long 

 since that he would never trust his life in the hands of a care- 

 less fellow, who, by throwing a pocket-handkerchief on the 

 lever of a safety-valve, might blow Up the vessel. Prejudice 

 of this kind might be removed and real danger prevented, by 

 means of a small steam-pipe carried from the boiler to a ther- 

 mometer properly graduated in the cabin. The force of steam 

 in the boiler would then be apparent to the passengers, and 

 the most timid be released from apprehension of danger. A 

 table for that purpose is easily calculated. 



