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Arts and Manufactures. 299 
No. 6. 8 feet focus, 6 inches aperture, price 4800 florins. This is 
the size which has been purchased for the Philadelphia and West Point 
observatories. 
o. 7. 6 feet focus, 52 lines aperture, price 2200 florins. 
No. 8. 5 feet focus, 48 lines aperture, price 2000 florins. 
All the preceding dimensions are French, which are greater than 
English measure. 12 French inches are equal to 12°79 English inches. 
VY. Arts anp MaNnurFAcTURES. 
1. Effect of Heat on the Tenacity of Iron; by Prof. W. R. Joun- 
son, (from the Report on the strength of materials for steam-boilers, 
1837.) —The following table exhibits the effect of heat on the tenacity 
of iron, both while actually hot and also subsequent to the application 
of a strain at high temperature. The comparisons are made on thirty 
two different specimens of iron, the origin of which is designated in 
the first column of the table. The page of the report of the sub- 
committee of the Franklin Institute, on the strength of materials for 
steam boilers, published in 1887, where the detail of the experiments 
is found, is given in thesecond column. The temperature at which either 
the “ hot fracture” or the hot strain was made on each bar, and which 
produced the strengthening effect of ‘* thermotension,” is contained in 
the third column. The fourth contains the number of trials made on 
each specimen of iron to ascertain its strength in its ordinary state and 
temperature, as itcame from the hammer or the rolls, and before being 
put under strain at a high temperature. Column fifth shows the num- 
ber of times the specimen was broken or at least strained at the tem- 
perature marked in column third. Column sixth gives the number 
of fractures made on the specimen to obtain the average strength after 
being heated, strained and then cooled again to ordinary temperature. 
Columns seven, eight, and nine contain the absolute strength given in 
the three different states respectively. Column ten exhibits the per 
centage increase of strength by treatment with thermotension, and 
eleven the difference in strength between the iron at ordinary tempera- 
ture in its original state, and that which it possessed while heated as in 
column third. In three cases only does it appear that the strength 
had been diminished by heating up to the point at which the trials were 
made. One of those trials was at 766°, one at 662°, and the third at 
552°. The average temperature at which the effect was produced was 
573-7°, at which point the eleventh column shows that the strength of 
thirty varieties of iron, was 5°9 per cent. greater than at ordinary tem- 
peratures, say at 60 or 80 degrees. 
It also appears that the average gain of tenacity in thirty two sam- 
ples of iron, by the process above mentioned, was 17°85 per cent., 
ranging from 8:2 to 28-2 percent. It will be found on reference to 
