178 
Steam Engine* 
safety- v^lve, so that those who attend the boiler will know 
with sufficient precision, by looking at the thermometer, 
how they ought to feed the fire ; and, moreover, the rela- 
tion between the temperature and the expansive force be- 
ing known, the danger of accidents from the safety-valve 
becoming deranged will be lessened, for the workman 
will naturally be led to notice whether the safety-valve 
acts freely when the thermometer has risen to the degree 
that answers to the weight with which the valve is loaded 
for working. I have found by actual experiment, setting 
out from the boiling point, or two hundred and twelve de- 
grees of the thermometer, commonly employed in this 
country, which is that of Fahrenheit, at which degree 
steam of water is only equal to the pressure of the atmo- 
sphere, that in order to give it an increased elastic force 
equal to five pounds the square inch, the temperature must 
be raised fifteen or sixteen degrees, or to about two hun- 
dred and twenty-seven and a half, when the steam will 
have acquired a power to expand itself to five times its 
volume, and still be equal to the atmosphere, and capable 
of being applied as such in the working of steam engines 
according to my said invention. And with regard to va- 
rious other pressures, temperatures, and expansive forces 
of steam, the same are shown in the following table : 
