128 STRAINS IN THE HULL OF A SHIP AT SEA, 



locks, they sometimes claim that the ship is drawing as much as two or three inches more at 

 the ends than she would if the temperature of the sun did not have so much effect on the 

 decks, and I would like to ask Mr. Howard if he noted that. (These boats are six hundred 

 feet long.) 



Mr. Howard: — In regard to the features which led up to making these tests, I will 

 say that for some time I have been engaged in the examination of engineering structures, 

 railway bridges, buildings, and pavements and strain gauge observations have been the means 

 by which the information was acquired. In this city, observations have been made on the 

 Bankers' Trust Building, a limited number on the Woolworth Building, on the main columns. 

 The Missouri River Bridge, at Kansas City, afforded an example of strain gauge observa- 

 tions on a large, modern riveted structure. Street pavements of Cleveland, Ohio, and 

 Kansas City, Mo., afforded additional opportunity for observations, and on earlier occa- 

 sions, very much earlier than these, there were measurements made on rails under the weight 

 of engines, noting the effect of different wheel loads, experiments being conducted on the 

 Burlington, Pennsylvania and the Boston & Albany Railroads. A strain gauge for measur- 

 ing dead loads was first devised for laboratory work, and subsequently modified for field 

 use, while this small scissors gauge was the last devised. This was gotten up primarily to 

 observe the strains on steel rails under the weights of locomotives and cars — the one here 

 shown (Mr. Howard displays a scissors gauge). Some modifications are expected to be 

 made, and to get it down to somewhat smaller dimensions. It is now only three inches 

 long, and of such shape that it may be put on the base of a rail and observations made at 

 slowly moving loads on the fiber stresses developed. 



The question of the accuracy and reliability of the instrument is, of course, one of the 

 first things to be considered. As far as I have been able to judge, it performs the same func- 

 tions on each occasion. The instrument, however, is not one of the easiest to be read, but 

 modifications will be made which are expected to improve that feature and permit greater 

 certainty about the finer subdivisions. I think if we now measure 1/50000 of an inch re- 

 liably we are doing pretty well, but can, under some circumstances, do better. 



The gauge was used for the first time on the deck plates of the Ancon. It is arranged, 

 as you will see, with flexible joints. The fulcrum plates are thin, flexible steel plates, so 

 that the instrument can be used where there is considerable dust, as there is no opportunity 

 for dust to get into any of the working parts. The behavior of the gauge, I think, was the 

 same on different occasions. If that were the case, then it comes to a question of calibra- 

 tion or rating of the instrument, and that admits of being done in the laboratory with pre- 

 cision. On the whole, the instrument, or some slight modification of it, seems to be a prac- 

 ticable affair. 



In regard to changes of temperature affecting the draught of the boat, no observations 

 were made. The effect on the deck of the Ancon, while receiving cargo, in which there was 

 a change of stress of some 5,000 pounds per square inch, which I attribute to temperature 

 causes, would lead one to suppose that the draught might be changed and made more or less 

 amidships, according to the temperature of the deck. I think that theory would certainly 

 be tenable. 



The Chairman: — 'Gentlemen, I am sure that you will desire to express your thanks 

 to Mr. Howard for his valuable paper, and I should be glad to entertain a motion to that 

 effect. It has been moved and seconded that the Society extend a vote of thanks to Mr. 

 Howard for his very able paper. It is so ordered. 



