422 PROCEEDINGS OF THE AMERICAN ACADEMY 



Rule for Cylindrical Cast-iron Pillars. 



For practical purposes we may divide the use of cylindrical cast-iron 

 pillai's into three cases : — 



1. Pillars with rounded ends, or put up as they come from the 

 founder, or with only the prominent irregularities at the ends chipped 

 off, or however the ends may be, if the weight is very unequally dis- 

 tributed over their surfaces, or if unequal settlements may be appre- 

 hended. When the designer of the pillars has no control over the 

 execution of the work or any guaranty that his directions will be mi- 

 nutely followed, his only safe course will be to consider them in this 

 case. The weights given in the tables are the safe weights the pillars 

 will support in this case. 



2. Pillars with the ends turned in a lathe, to planes at right angles 

 to the axes, and put up with ordinary care, so that the weight will be 

 distributed over the whole area of the ends ; the pillars being made and 

 put up under the eye of the person responsible for their sufficiency, or 

 with such other guaranty for faithful workmanship as may be satisfac- 

 tory to him. In this case, it is assumed that the safe weight is one and 

 a half times that for a pillar with rounded ends, and may be found from 

 the tables by adding one half to the tabular weight. 



3. Pillars with the ends finished, and put up with the degree of per- 

 ^fection attained in Hodgkinson's experiments on pillars with flat ends. 



The safe weight in this case is three times that given in the tables. 



Note. The tables give the dimensions of several pillars of nearly 

 equal strengths, from which, of course, may be selected the pillar 

 deemed most suitable for the intended purpose. If the pillar is made 

 a little smaller at one or both ends than in the middle, its strength will 

 be nearly the same as that of a cylindrical pillar of the same length and 

 of a diameter equal to its middle diameter. 



Example. Required the dimensions of a pillar 12 feet long, the 

 greatest load to be supported by it being 25 tons. 



If in the first case, we find at the page of the table headed, " Cylin- 

 drical pillars of cast-iron 12 feet long," taking the tabular weights, 

 nearest to, but not less than, 25 tons, that if solid, the pillar must be 6 

 inches in diameter ; if f inch thick, 1^ inches in diameter ; if 1 inch 

 thick, GJ inches in diameter, &c. 



If in the second case, take f of 25 tons, which is 16.67 tons ; pro- 

 ceeding in the same manner as in the first case, we find that, if solid, 



