BAROMETRICAL AND METEOROLOGICAL OBSERVATIONS. 183 



can therefore always be detected in the air by delicate instruments, while even in the 

 Mississippi Valley, in the drier climate of the summer months, frequently not the 

 slightest trace of 'it is indicated by the same instruments, us I am informed by Dr. Ad- 

 Wislizenus, of Saint Louis, who has lately commenced an interesting series ot experi- 

 ments npon this subject In the arid climate of Utah the air conducts the electricity 

 still less, and even the parched pulverulent soil appears to become a non-conductor. 

 Thus the electricity is accumulated where it is developed. Not only do woolen clothes, 

 buffalo-robes, and all sorts of peltry, and even the saddle-blankets on the horses become 

 highly charged, but the glass on wood-cased pocket-compasses becomes so electric that 

 the needle adheres to the glass and persistently refuses to work, and the equilibrium 

 cannot be restored by merely touching the glass with the hand. Where thus every 

 part of the instruments, and the body and clothing ot' the observer are apt to be elec- 

 tric, and the soil and air are non-conductors, all the delicate magnetic observations 

 become exceedingly difficult to take. 



I cannot conclude these remarks without mentioning a phenomenon familiar to 

 all the settlers along the foot of the Wahsatch range. During certain seasons, regu- 

 larly every evening soon after sunset, a wind rises, blowing from the summit ot the 

 mountains down the canons, toward the wide longitudinal valleys at their base. It is 

 by them called canon-wind, and finds its explanation in the circumstance that in the 

 evening when the other winds generally lull, the radiation of heat of the bare dry sod 

 of the valleys, and consequently the upward movement of the heated air continues tor 

 several hours, and the equilibrium is restored by the afflux of colder air from the 

 mountain summits by the channels of the narrow side-valleys, in which the tempera- 

 ture is depressed by the evaporation of their streams, which makes a great deal of hea t 

 latent. This phenomenon bears resemblance to the land and sea breezes on the coast. 

 Another phenomenon of frequent occurrence near Camp Floyd are whirlwinds, 

 which for months may be seen nearly daily traversing Cedar Valley in its longitudinal 

 direction from north to south. They have no great diameter, but considerable height, 

 and may readily be followed with the eye by the high cylindrical column of dust which 

 they raise. When they passed our barometrical station. I observed several times that 

 the mercurial column fell momentarily, and then rose again to its former height; all 

 within the few seconds occupied by the passage of the whirl. I never observed, instru- 

 mentally, the quantity of this fall, but it cannot have been less than 0.1 inch, and per- 

 haps it was much larger. The fall of the barometer is partly caused by the upward 

 movement, and thus diminished pressure of the air, of which the height of the column 

 of dust affords a proof, but I explain it principally by the fact that the whirl, being 

 formed by a body of air in violent motion, does not exercise the pressure correspond- 

 ing to a similar column of air at rest or comparative rest outside the whirl. Tins is 

 in strict conformity to the laws of pneumatics, and analogous to the laws of the differ- 

 ence of the static and dynamic pressure of fluids. A third cause is to be found in the 

 circumstance that the progressing whirl, imparting its rapid rotary motion to bodies of 

 air before comparatively at rest, tears them off from the main body of the ah, which 

 is unable to join in that motion so rapidly as not to exhibit a slight expansion and con- 

 sequent diminution of the pressure. The causes of the frequent occurrence, and of 



