RECOMMENDATIONS. 473 



3. Experiments on the solar and terrestrial radiation. {Re- 

 port, vol. i. p. 222.) 



4. Observations on the horary oscillations of the barometer, 

 at considerable heights above the sea. This more particularly 

 applies to places near the equator'. 



5. Additional observations to determine what is the influence 

 of the moon on the height of the barometer. {Report, vol. i. 

 p. 234. See also Arago, Annuaire for 1833.) 



6. The application of the hygrometric correction to the ba- 

 rometric formulae for heights. {Report, vol. i. p. 254.) 



7. Observations on the phaenomena of wind at two stations, 

 at considerably different elevations, (p. 249.) The direction of 

 the wind should be noted in degrees, beginning from the south 

 and proceeding by the west. 



8. Magnetical observations, regularly conducted, especially 

 with a view to auroral phaenomena. 



OPTICS, 



* That a sum not exceeding £50 be appropriated to the 

 construction of a telescopic Lens, or Lenses, out of rock-salt, 

 under the direction of Sir David Brewster. 



Desiderata noticed in Sir David Brewster's Report. 



The determination of various constants, namely, 

 L The refractive indices of the two pencils in all crystallized 

 bodies, measured in reference to definite points of the spectrum. 



2. The angles at which light is polarized by reflection from 

 crystallized and uncrystallized surfaces. 



3. The inclination of the resultant axes of crystals having 

 double refraction, for different rays of the spectrum. 



4. The dimensions of the ellipse which regulates the polariza- 

 tion of metals and their alloys. 



5. The circularly polarizing forces of fluids and solutions. 



6. The refractive and dispersive powers of ordinary solid and 

 fluid bodies, measured according to the method of Fraunhofer. 



7. Experimental determination of the effects of the absorp- 

 tion of light by gases upon the light of the fixed stars, (p. 322.) 



^ Those who may possess such observations, continued for one or more weeks, 

 with observations of the temperatures of the mercury and of the air, and the 

 probable corresponding temperatures of the air at the level of the sea, are re- 

 quested to transmit them to Professor Forbes, Edinburgh. The local position 

 of the point of observation should also be noticed. 



