350 



SCIENCE. 



[N. S. Vol. I. No. 13. 



independent determinations by the repre- 

 sentatives of both governments. This was 

 not practicable in the longitiide determina- 

 tions, but in the latitudes, running the 

 parallels and locations of the numerous 

 monuments, it was strictly carried out. .The 

 mean diiference in the location of the 258 

 monuments, was less than three-tenths of a 

 metre ; the maximum difference was onlj^ 

 1.8 m., which occurred in locating a point 

 about midway between two old monuments 

 100 miles apart, and over a very rough 

 mountainous country, where the distances 

 between water holes was over 60 miles. 

 The angular variations of the lines run by 

 the two parties at this poiut was a little 

 more than three seconds. 



The final results from the astronomical 

 observations were required for immediate 

 use on the ground ; to permit the computa- 

 tions the mean declinations for the stars for 

 latitude had been furnished by Professor T. 

 H. Safford, of Amherst. In this way the 

 latitude and azimuth were always available 

 within three or four days after the observa- 

 tions were completed, a feature of such work 

 that, it is believed, has not heretofore been 

 attempted. Mr. Mosman promises that a 

 list of the stars furnished by Professor Saf- 

 ford, some 600, will be published in the re- 

 port of the commission, to be available for 

 future work in the same latitude. 



In locating the intermediate monuments 

 the commission made use of the stadia, with 

 gratifying results. On the parallel of 31° 

 47' for a distance of 100 miles both chain 

 and stadia were used for the purpose of com- 

 parison. It was found that the stadia was 

 m^uch more reliable than the chain, even on 

 the desert, and in a rough country was much 

 superior. The whole line was measured 

 by both the American and Mexican engi- 

 neers independently ; when the two results 

 for any distance differed more than one part 

 in 500, remeasurements were made by steel 

 tape or triangulation to discover the error. 



Many Imes determined by triangulation 

 were compared with the lengths determined 

 by stadia, and the results showed that the 

 stadia measurement could be relied on 

 within one part in 1000. One line of 45 

 miles measured over rolling sand hills dif- 

 fered by one part in 1800 only. 



In addition to the astronomical work, a 

 strip of topography was surveyed on the 

 American side 2h miles wide, and a line of 

 levels was run with the wye level from the 

 Rio Grande to San Diego, giving the eleva- 

 tion of each monument above mean tide of 

 the Pacific Ocean. The levels were checked 

 at Yuma with R. R. levels fi-om San Fran- 

 cisco, showing the infinitismal discrepancy 

 of two hundredths of a metre, probably an 

 accident. At the Rio Grande there is a 

 discrepancy of about two metres, but the 

 datum plane for the R. R. levels at this 

 place is not known. O. 



THE NATUBE OF SCIENCE AND ITS BE- 

 LATION TO PHILOSOPHY. 



If any one should ask me, ' What is phj's- 

 ics ? ' I would tell him to study in the phys- 

 ical laboratory for ten years and then 

 what he had learned by the time he was 

 through woiild be the nearest he could get 

 to an answer to the question. So to the 

 question, ' What is science ? ' I can give no 

 other general answer than that to anyone 

 it is just what he knows about it. I can, 

 however, give as a particular answer what 

 I have in my own experience found science 

 to be. 



Science consists of weighing evidence and 

 stamping each statement with an index of 

 its reliability. That the sun moves around 

 the earth is, according to the evidence at 

 present produced, a statement with a relia- 

 bility of 0. That the earth moves around 

 the sun, we at the present day stamp as 

 certain. That Mars contains living beings 

 is to-day stamped as quite improbable. 

 On the scale of probability where means 



