abstracts: geodesy 585 



to 1.55 calories in June. When clouds were near the sun but did not 

 obscure it these rates were increased momentarily by as much as 0.15 

 calorie. For the period September, 1907, to September, 1914, the maxi- 

 mum intensity of direct solar radiation at normal incidence at noon 

 varied from 1.37 calories in January to 1.50 calories in May and 

 September. 



The measurements show that at mid-day in summer about 18 per 

 cent of the total radiation received on a horizontal surface was diffuse 

 sky radiation. With a hazy sky about one-third of the total daily 

 radiation was received in this way, as compared with one-tenth on a 

 very clear day. 



The measurements also show that at noon, on a clear mid-summer 

 day, each square yard of horizontal surface at this station received heat 

 energy at the rate of about 1 kilowatt, and that the total received from 

 sunrise to sunset was equivalent to about 5 kilowatt-hours. From the 

 middle of March to the end of August, on the clearest days, the total 

 energy received was equivalent to 4 kilowatt-hours, or more. 



H. H. K. 



GEODESY.^ — Primary triangulaiion on the one hundred and fourth merid- 

 ian, and on the thirty-ninth ■parallel in Colorado, Utah, arid Nevada. 

 William Bowie. Special Publication No. 19. Coast and Geodetic 

 Survey. Pp. 163. 1914. 



This volume contains the geographic positions and the descriptions 

 of about 600 primary triangulation stations, which are located along the 

 104th meridian of longitude in Colorado, Wyoming, the Dakotas, and 

 Montana, and along the 39th parallel of latitude in the states of Colo- 

 rado, Utah, and Nevada. 



The field work of the 39th parallel triangulation was completed in 

 the late nineties, and a report on that work appeared in 1899 as Coast 

 and Geodetic Survey Special Pubhcation No. 4. Since that date a 

 standard datum for all connected triangulation in this country was 

 adopted and called the United States Standard Datum. In 1913, when 

 this datum was adopted by Mexico and Canada, its name was changed 

 to the North American Datum. It is not identical with that on which 

 the Transcontinental triangulation was originally based, hence the neces- 

 sity of publishing the new positions in Special Publication No. 19. 



The field work on the 104th meridian triangulation was done during 

 one season of about six months by two observing parties. As this arc 

 is 720 miles in length, the rate of progress for each par.ty was about 60 

 miles per month. 



