WIND OBSERVATIONS 17 



measure solar radiation at sea, though in the hands 

 of an interested observer Wilson's radio-integrator 

 might be tried with some prospect of success. It would 

 require to be exposed to the sky above all awnings. 



Wind Observations. 



To observe the true direction of wind in a steamer 

 running at high speed requires the skill born of ex- 

 perience for judging by the crests of the waves in rough 

 weather and by the rippling of the surface when smooth. 

 An instrument by which the true direction can be ascer- 

 tained from the apparent direction and the course of 

 the vessel, has been devised by Professor A. L. Rotch, 

 of Harvard, and is described in the Quarterly Journal 

 of the Royal Meteorological Society, vol. xxx., 1904, 

 P- 3 I 3- The force of the wind at sea is always esti- 

 mated, not measured, generally by the curl of the 

 waves ; allowance must be made for the speed of the 

 vessel and the angle of her course, as well as for the 

 speed of the wind and its true direction (which is 

 deduced from the curl of the sea). When there is a 

 following wind and the smoke rises vertically, as does 

 occur occasionally, the speed of the ship gives the 

 velocity of the wind with the exactness of an anemo- 

 meter on land. With other winds the speed of the 

 ship must be added to or deducted from the estimated 

 velocity, unless the estimation is made by observing 

 the effect of the wind on the waves. The Robinson 

 cup anemometer cannot give trustworthy results at 

 sea, as the spindle must be kept vertical if its indications 

 are to be of any value. Experiments might well be 

 made with the Dines pressure-tube anemometer, or 

 some variation of it ; but this belongs at present to the 

 region of research rather than of observations. 



