Mat 28, 1915] 



SCIENCE 



803 



tion than formerly and (6) more thoroughly roll 

 the wearing course prior to the first application 

 of bituminous material. 



Bituminous concrete pavements have increased 

 in popularity in many sections of America. There 

 has been a general tendency to use carefully heated 

 aggregates and employ mechanical mixers. Bi- 

 tuminous materials of lower penetration than 

 form.erly are used in bituminous concrete, the 

 aggregate of which is composed of one product of 

 a stone-crushing plant, the sizes of stone ranging 

 from i in. to li in. The largest contract for this 

 type of construction during 1914 was the Ashokan 

 Highway, 37 miles in length, built by the board 

 of water supply of New York City. 



The third session was held on the morning of 

 Thursday, December 31, Vice-president Dr. Fred- 

 erick W. Taylor and Mr. O. P. Hood in the chair, 

 with an attendance of about 70. The program of 

 the session was as follows: 

 Vice-presidential Address: Safety Engineering: 



O. P. Hood. 



Engineering and Industrial Regulations for Fro- 



'moting Safety in Industrial Establishments: 



John Pkice Jackson. 

 Recent Developments in Precise Leveling : William 



Bowie. 



There should be in each city and state and 

 throughout the whole country connected systems 

 of leveling to form the basis and give the datum 

 for the ordinary spirit or wye leveling. 



The nation has, at present, about 31,000 miles 

 of precise leveling with more than 13,000 substan- 

 tial bench marks. The elevations in the precise 

 level net are referred to mean sea level. The mean 

 surface of the water at the starting points was 

 derived from long series of tidal observations. 

 Mean sea level is the natural and the best datum 

 for a level net. In the first place, it is a funda- 

 mental datum, for it can be reproduced; again, 

 wdth it, leveling can be started at many places with 

 certainty that when the different lines are joined 

 the agreements will be close. Also, leveling by 

 different nations will agree when it is connected 

 on the international frontiers. 



There should be only one datum for the whole 

 country, and this is only possible after the level 

 net has been extended to such an extent that no 

 place is far from a precise level bench mark. 



The instrument used by the Coast and Geodetic 

 Survey in its precise leveling is generally known as 

 ■the "United States Coast and Geodetic Survey pre- 

 cise level." Its noteworthy features are that it is 



made of an alloy of nickel and iron which has a 

 very low coefiicient of expansion; its bubble is set 

 down into the telescope near the axis of collima- 

 tion; and its binocular system, by which the ob- 

 server can see the bubble, cross wires and rod at 

 the same time. The instrument was designed and 

 made in the Coast and Geodetic Survey Oface. It 

 has proved very effective in enabling the observer 

 to avoid or eliminate many of the errors which 

 were in the leveling done with the older types of 

 instruments. 



All lines are run at least twice, in opposite di- 

 rections. To be acceptable the two runnings of a 

 section must agree within four millimeters times 

 the square root of the distance in kilometers. 



The average progress in the work per month is 

 now about 86 miles for each party. The maxi- 

 mum progress ever made by one party was in Oc- 

 tober, 1914, when 148.3 miles were completed. 

 The rapidity with which leveling is now done is 

 due mainly to the use of the motor velocipede cars 

 as the means of transporting the members of the 

 party and to the more efficient organization and 

 management of the leveling parties. 



The great accuracy of the leveling is indicated 

 by the probable error of the elevation at St. Paul, 

 Minnesota (the least accurately known place in 

 the net) resulting from the 1912 general adjust- 

 ment of the level net of the whole United States, 

 which is only ±0.065 meter (±0.21 foot). The 

 average correction to the lines forming the net for 

 loop closure is about 0.15 millimeter per kilo- 

 meter. An investigation of the small systematic 

 and accidental errors in the precise leveling indi- 

 cates that, when the ground is sloping, more accu- 

 rate results are obtained on a cloudy afternoon, 

 with a moderate wind blowing, than under the re- 

 verse conditions. When the ground is nearly level, 

 the time of the day and the atmospheric and 

 weather conditions do not seem to have any mate- 

 rial systematic effect on the line of levels. 

 The Engineer Out in the World: Martin Schrei- 



BEK. 



The Teaching of Industrial Economics and Man- 

 agement to Engineering Students: Hugo Diemee. 

 Recent engineering curricula show that instruc- 

 tion in industrial economics and management is 

 being introduced in an increasing number of in- 

 stitutions. Examples are cited from the curricula 

 of a number of well-known universities and col- 

 leges. Statistics regarding the positions held by 

 the membership of the leading national engineer- 

 ing societies show that more than half of the com- 



