716 



SCIENCE 



[N. S. Vol. XLII. No. 1090 



The following table gives data for leveling 

 done under different conditions of tbe sky. 

 The letter stands for cloudy and S for sun- 

 shine or clear. 



RUNNINGS IN CLOUDY AND CLEAK WEATHER 



Steep Grades Low Grades 



Number of sections 56 217 



C~S, total, positive + 159.2 + 473.1 



Mean discrepancy + 2.84 + 2.18 



Number of sections 45 228 



C-S, total, negative — 85.1 — 482.3 



Mean discrepancy — 1.89 — 2.12 



Number of sections 101 445 



Mean discrepancy 2.42 2.15 



Accumulated discrepancy . . + 74.1 — 9.2 

 Mean accumulation per sec- 



iion + 0.73 — 0.02 



The mean accumulated discrepancy here is 

 -^- 0.Y3 for the steep grades while for the low 

 •grades it is practically zero. 



It is the general belief among geodesists that 

 the leveling under a cloudy sky is practically 

 free from systematic errors resulting from at- 

 mospheric conditions. Therefore it would ap- 

 pear that the leveling under a clear sky causes 

 the observed differences in elevation on steep 

 grades to be too small. 



In the following table are given data for the 

 steep sections which had one running in clear 

 and the other in cloudy weather, but the data 

 are arranged in two groups, one where the 

 running in sunshine was made in the morn- 

 ing called (SA) while the other has the run- 

 ning in sunshine made in the afternoon (8P) : 



EDNNINGS WHEN CLOUDY AND ON CLEAE MOENINGS 

 Steep Grades Low Grades 



Number of sections 56 240 



C-SA, accumulation per section. -|- 0.24 -\- 0.11 



EUNNINGS WHEN CLOUDY AND ON CLEAE AFTEENOONS 

 Steep Grades Low Grades 



Number of sections 45 215 



C-SP, accumulation per section. '-|- 1.34 — 0.21 



The number of sections on steep grades is 

 too small to warrant our drawing any definite 

 conclusions from the data given. The indica- 

 tion from the steep section is that the after- 

 noon running gives a value lower than the 

 m.orning value. 



The average accumulated values of 0-8A 

 and C-SP for the sections with low grade are 

 small, -\- 0.11 millimeter per section in the 

 former and — 0.21 millimeter per section in 

 the latter. These sections are quite numerous 

 as compared with the number of steep sections, 

 and should no doubt be given some considera- 

 tion before coming to a decision as to whether 

 the morning or afternoon runnings in sun- 

 shine give the larger differences. 



The data in the following table show some 

 relations between the systematic errors of 

 leveling and calm and windy weather. The 

 letter C stands for calm and W for wind. 



EUNNINGS IN CALM AND IN WIND 



Steep Grades Low Grades 



Number of sections 63 277 



C-W, total, positive -|- 140.0 + 544.3 



Mean discrepancy -f 2.22 -j- 2.0 



Number of sections 75 345 



C-W, total, negative — 199.8 — 757.4 



Mean discrepancy — 2.66 — 2.20 



Number of sections 138 622 



Mean discrepancy 2.46 2.11 



Accumulated discrepancy . . — 59.8 — 203.1 

 Mean accumulation per sec- 

 tion — 0.43 — 0.33 



Both for the steep and low grades the run- 

 nings during wind give on an average greater 

 differences in elevation between the ends of a 

 section than the runnings during calm. The 

 average is almost as large for the low grades 

 as for the steep ones. This can not be con- 

 sidered to be a general rule for other factors 

 may and probably do influence the results. 

 All of the lines are in the western portion of 

 the United States where it is usually more 

 windy in the afternoon than in the morning. 

 Calm is infrequent there in the afternoon. 

 Therefore the value of 0-W would be some- 

 what confused with the value of P-A. 



If both runnings are made in the forenoon 

 or both in the afternoon, then the values of 

 C~W should be practically free from the effect 

 of the time of the day. In the following table 

 there are given the data for such sections, the 

 amount of grade not being considered. 



