A. B. poy on high and low pressure Boilers. 315 
m the — results, that the Jow pressure, 
is n han three times as safe as one of the high 
pressure kind ; or, that the safoty of the low pressure boiler- 
is fe thatof the high pressure boiler in me Proportion of 163 
° Bat it can be shown that either engine can be made 
‘tirely safe; and that one kind is not, in fact, any more liable 
to explode than the other. 
To prove this we have, (by mechanics.) the thickness of a 
low pressure boiler 90 inches in diameter, capable of resist- 
5X1 
ing 10 lbs. per square ineh, <a 18 = 015 In. ; and, 
that of a high pressure boiler 30 ‘deh in diameter, Sepals 
of resisting 150 Ibs. per square inch = a= -075 inches. 
And, now, if we multiply the first of these results by 10, 
we shall have .15in. for the thickness of a low pressure 
boiler capable of resisting 10 times the usual working g pres- 
_ sure ; which is 90 lbs. above the usual working p reassure. 
And the thickens of a high pressure ee capable of 
ag ray ie times the usual working pressure 
0x10 
=.75 in.; and, lastly, the thickness of a 
oe 000 
high pressure boiler capable of resisting 90 lbs. per per square 
inch above the usual warling pressive is ='° ee 4 
30,000 
12 in 
Fienick: as itis fully pigeticable to make a boiler of a thick- 
ness equal to any of the foregoing results, uy eiein that one 
kind of engine may be made just as safe as tl 
I shall merely add, that as the tenackee’ ro) etal is dimin- 
ished by an increase of temperature, the tenacity in the case 
of the high pressure boiler should have been taken some sd 
than in the case of the dow pressure boiler.* 
at As no experiments fave ever, to my iis wlleagé, been made for de- 
termini decrease of the tenacity of s corresponding with a 
ven ease of temperature, and as this, in my es ion, i 
ject of considerable philosophical interest, I will respectfully suggest to 
the gentlemen who compose the present committee, that they ha ave 
such experiments instituted, as may, if possible, detect the law, by which 
the tenacity decreases, during a given increase of temperature. 
