606 



SCIENCE 



[N. S. Vol. XXXII. No. i 



from land, very little activity was collected; 

 particularly was this the case on December 11, 

 14 and 18. The region in which this happened 

 was a very calm one, and the air had probably 

 not been in contact with the land for many 

 days. Mr. Kidson is inclined to think, there- 

 fore, that the land is the chief source of the 

 radio-active matter in sea air. This is what 

 would be expected from determinations of the 

 radium content of sea water. The fact that 

 Mr. P. ri. Dike, the observer on the Galilee 

 in the Pacific, could obtain no evidence of 

 radio-activity except near land, also points to 

 this conclusion. The Pacific Ocean being of 

 so much greater extent than the Atlantic, 

 there should be much larger tracts over which 

 the air had lost any radio-activity got from 

 the land. The absence of thorium emanation 

 would tend to confirm this theory. 



It is easy to understand that the air in the 

 North Atlantic between Newfoundland and 

 England may at times have all been over land 

 surfaces within a week. This may account for 

 the results obtained by Professor Eve in this 

 region." Observations comparing the amounts 

 of radio-activity over land and ocean are much 

 needed. 



0. Atmospheric Refraction Ohservations. — 

 These observations consisted in the determi- 

 nation of the " dip of the horizon," being made 

 for the purpose of controlling the corrections 

 to be applied to the astronomical observations 

 on account of atmospheric refraction. The 

 observer was J. P. Ault, the navigating officer 

 on the first cruise, Pulfrich's dip measurer, 

 made by Zeiss, being used, in which, by the 

 aid of prisms, the two horizons to the right 

 and to the left are seen as two parallel vertical 

 lines in the field of view of the small tele- 

 scope, the distance apart of the lines being 

 equal to twice the angular value of the dip of 

 the horizon, read off in minutes by means of 

 a scale. 



The corrections found on the values ob- 

 tained from atmospheric refraction tables 

 were, in general, negative, reaching a maxi- 

 mum of — 1'.02, showing the tabular value to 

 be too large, however, on the portion of the 



= A. S. Eve, •■ Terr. Mag.," v. 15, 1909 (25). 



cruise between Bermuda and New York the 

 corrections in the mean are positive, the maxi- 

 mum being + 1'.23. The dip of the horizon 

 being a correction which is applied directly to 

 an observed altitude of a celestial body, if 

 then in case the latitude is obtained from 

 meridian altitudes it would be in error by the 

 same amount as the dip correction, hence in 

 the maximum 1| of a minute of arc or of a 

 nautical mile, or nearly IJ statute miles. The 

 error in longitude will vary from one minute 

 to over three minutes of arc, allowing a celes- 

 tial body an azimuth of over thirty-five de- 

 grees from the meridian and for a range in 

 latitude from twenty degrees north to fifty de- 

 grees north; for extreme conditions the error 

 may even be greater. 



It is thus seen that it is highly desirable 

 for the mariner to have accurate tables of at- 

 mospheric refraction, especially near land, 

 where an error of a mile or two in the ship's 

 position is a matter of grave importance. 

 In fact our attention to the need of such ob- 

 servations was first called by mariners them- 

 selves, who have found at various times when 

 nearing the coast, where the opportunity was 

 afforded to check their astronomical positions 

 by land objects, that their positions were out 

 presumably due to the tabular values of at- 

 mospheric refraction. How far the refraction 

 corrections may depend upon prevailing 

 meteorological conditions must be left for 

 future examinations when additional data 

 are at hand. 



D. Gravity Ohservations. — Suggestions have 

 been received from various sources that it 

 would be highly desirable to include, if pos- 

 sible, gravity work on the Carnegie. In 1905 

 I consulted Professor Helmert, director of the 

 Geodetic Institute at Potsdam, as to the possi- 

 bility of attempting such work on the Galilee, 

 which at the time was chartered, as may be 

 recalled, for the magnetic work in the Pacific 

 Ocean. One of his assistants. Dr. Hecker, 

 had employed the method of getting gravity 

 results at sea by determining the temperature 

 of the boiling point of water, deducing there- 

 from the corresponding atmospheric pressure 

 and comparing this with the observed mercur- 



