56 



KANSAS Academy of Science. 



TIDE CHECKS. 



Note. — Lieut. Gardner, in his "Elevations of Datura Points," 1875, (pages 643, 644 and 653,) reports 

 errors as follows : 



(o) 9.9 feet, Portland to New Orleans via Chicago, 2,100 miles, or 0.0048 feet per mile. 



(6) 2.44 feet from New York Bay to New Orleans via Chicago, 1,800 miles, or 0.0013 feet per mile. 



(c) 4.61 feet, Raritan Bay to New Orleans via Chicago, 1,800 miles, or 0.0025 feet per mile. 



(d) 25.0 feet, Portland to San Francisco via Chicago, 3,500 miles, or 0.0071 feet per mile. 



(e) 26.0 feet. New Orleans to San Francisco via Kansas City and Denver, 3,200 miles, or 0.0081 feet 

 per mile. 



Mr. S. D. Mason, Principal Asst. Engr. N. P. R. R., under date of Nov. 19, 1885, reports an error of 

 " about 4 feet," ( not yet definitely determined,) from Lake Superior, at Duluth, to Commencement Bay, 

 at Tacoma, 2,0.33 miles, or 0.00185 feet per mile. The correctness of my results within the limits of my 

 stated errors is not corroborated by these errors reported from other roads, as they have no bearing 

 upon the St. Louis Directrix or any of my elevations, and are given here merely for a comparison of 

 errors per mile in levels. 



By the close results which have been obtained I am convinced that the necessity 

 for the excessive corrections applied by Mr. Gannett arose from the elevations re- 

 ported to him not having been corrected for breaks in datum planes. I do not offer 

 my results as evidence that railroad levels in mountainous regions are generally to 

 be depended upon within a hundredth of an inch per mile, nor would I intimate that 

 the close results over these particular circuits and check lines from the Missouri 

 river to the Pacific ocean prove the correctness of the old elevation of St. Louis 

 (428.29) and the Missouri river benches at Kansas City and Atchison, as stated by 

 Gardner in 1875, from Atlantic tide points; but in view of the fact that the recent 

 levels of the Coast Survey and Mississippi River Commission tend to lower the ele- 

 vation of St. Louis and neighboring points 13 and 15 feet respectively, the results 

 given in the second table above, and based upon Gardner's St. Louis datum, are of 

 special interest at this time, for to reduce St. Louis 15 feet would be to make the 

 "errors in feet" in my second table range from 13 to 19 feet. 



By using the Atlantic mean tide benches established in the Missouri river valley 

 twelve years ago and the most reliable line of railroad levels which I have at com- 

 mand, and which has but one break, I check from ocean to ocean ( mean tide to 

 mean tide) within three-quarters of an inch; and now come the Mississippi River 

 Commission and Coast Survey with their "levels of precision" and say the old 

 benches were too high by 15 and 13 feet respectively. I append Mr. Gannett's letter 



of Oct. 20, 1883: 



Department of the Interior, United States Geolouical Survey, ) 



Washington, Oct. 20, 1883. / 



Mr. H. V. Hinckley, Office Engineer A. T. <fe S. F. R. R. — Dear Sir: I am in receipt this morning of 

 your communication of the r2th, containing your list of carefully-determined elevations upon the line 

 of your road. Allow me to thank you in the warmest possible terms for this favor, and to assure you 

 that the fullest credit will be given for this valual>le piece of work. lam very much puzzled about 

 this change in the St. Louis Directrix, and the consequences it involves. There can be no mistake 

 about the tigures as I have received them from the Secretary of the Commission, and the change which 

 this makes is corroborated by the corresponding changes in the heights of Cairo and other points be- 

 low on the river, the heights of which were received from the Secretary of the Commission at the same 

 time. On the other hand, the checks westward from Kansas ('ity are thrown into confusion not only 

 upon your road but upon other lines. Very truly yours, Henry G.vnnett, 



Chief (leographer U. <S'. O. S. 



