the experiments is to a great extent due to the correct value of с = 19 tons.

As an illustration of the rules in (197) and (164), we may take Nos. 13, 14, in Table 44: then 95848 × 1·005 ÷ 1·262

3.6

F

= 61470 lbs., the value of F, or the breaking weight by flexure, as in col. 9. This requires correction for incipient crushing (163):-to find Cp we have 1·0052 × 7854 × 42560 = 33760 lbs. as in col. 10, hence 3 Cp 25320 lbs., and the rule Pc × Cp÷(F+ C) becomes 61470 x 33760 (61470 + 25320) =23910 lbs., the reduced breaking weight or value of Pc, as in col. 7.

=

=

- errors

Table 44 has been calculated in this way throughout the sum of all the + errors in col. 8 569 and of all the 52.5, giving on 15 experiments an average of (56.9 — 52·5) ÷ 15 = 0.293 per cent. only. The greatest + error = 13.8 per cent., and the greatest error 15.3 per cent. (959).

=

=

(202.) Searching as in (165) for the length of wrought-iron pillars with which the correction for incipient crushing becomes nil, beyond which length the rule must not be applied for reasons given in (164); we find that a pillar 1 inch diameter crushes with 7854 × 19 = 14.92 tons, the correction will therefore be nil when F 14.924 = 3.73 tons (169), which in a pillar with both ends pointed is due by the rule (199) to a length of 42.79 3.73 x 12 = 40.64 inches, or 40 64 ÷ times the diameter. With one end pointed and one flat 88.263.73 × 12 = 58 37 inches:_with both ends flat 133.83 73 x 12 71.86 inches, &c. With cast-iron pillars (165) we obtained for the same diameter 16.64, 25.04, and 31 78 times the diameter respectively, which differs remarkably from 40 64, 58 37, and 71 86 as found for wroughtiron pillars.

These ratios vary with the diameter as we found to be the case with cast iron (166), and as shown by Table 39, which has been calculated by the rule :

(203.)

LD

=

(Mr X D36÷Cp) x 12÷D.

In which the letters have the same significance as in (167).

TABLE 45.-Of the STRENGTH of WROUGHT-IRON CONN

159,400 45,800 30,130 25,800 21,800 16,500 16,500
12 80,600 79,800 45,790 44,900 34,360 28,700 25,960
2 105,000 128,000 65,030 72,400 50,280|| 46,400 39,000
24 133,000 197,000 88,290 111,000 70,000 70,900 55,270
2165,000 288,000 115,400 162,000 93,460 104,000 75,270

2 200,000 407,000 146, 200 229,000 120,850 147,000 95,620
3 237,000
313,000 151,100 200,000 125,400

31 279,000

10

13