21B [AsasHBLT 



as the sum of all these objections resolves them into three points, it 

 may be proper to state and refute the two first, and submit some pros- 

 pective arguments against the third. 



1st. The danger of lightning. 



The answer to this, is, that a large mass of iron having a direct 

 contact, or ready communication with the earth, furnishes at every 

 angle, and every salient point; a conductor which silently but safely 

 transmits the surplus or positive electric fluid from the air, to the 

 earth beneath it No proof is known to be on record that an iron 

 foundry or machine shop, has ever been struck by a descending mass 

 of the electric fluid in a thunder storm; though the undersigned has 

 stood by the w'orkmen in a large manufactory, and seen the lightning 

 playing about the points oi the cutting tools in the lathes, so severe 

 has been the storm raging around the factory; the inevitable mechan- 

 ical conclusion is, that the number of points separately, abstract, di* 

 vide, and disarm the most tremendous agent of destruction we are 

 yet acquainted with, and by quietly transmitting it to the earth, ren- 

 der it harmless. This objection was raised twenty-five years ago by 

 the then directors of the English East India Company, to the con- 

 struction of fire proof buildings for their mints, at Calcutta and Bom- 

 bay; but the experience of their successors has shown the contrary. 



The second objection is that the contraction by cold and expan- 

 sion by heat, will injure the walls of brick or stone, and will risk 

 disruption of the parts in a metal building. 



From 50° of Fahrenheit below zero, to 200° above zero, the con- 

 traction or expansion of a cast iron beam forty feet long, is only a 

 small fraction more than one quarter of one inch; and although this 

 exerts a power like freezing water, which nothing can withstand, it 

 is rendered harmless, by a provision for the ends to slide on their 

 beds in the walls, or on the tops of the intermediate columns, and 

 none of the parts are disturbed; and although the capacity of cast 

 iron to bear a blow, is somewhat lessened in severe cold, no fact is 

 known to prove, that the beam is affected by cold in the capacity to 

 bear the weight which it is generally supporting. 



Wrought iron expands and contracts more by the same degrees of 

 heat and cold, than cast iron; but these amounts are now so fully 

 known, that a competent engineer can provide for the differences, 

 when cast and wrought iron are employed together; and where 



