292 SCIENTIFIC EECORD FOR 1884. 



knowledge of the methods of determining the temperature and moistuie 

 of the air. He lays it down as a criterion by which to judge of the ex- 

 cellence of any thermometer shelter, that if we place within the shelter 

 a ventilating apparatus and read the thermometers both with and with- 

 out ventilation then the exposure is satisfactory if on the average no 

 greater difference occurs than ±0°.! C. He then states that the ex- 

 periments demonstrate that the motion of the thermometer through the 

 air as in the rotation and the sling thermometers or the movement of the 

 air past the thermometer, as in the Italian ventilated thermometer, is 

 a much less effectual method of overcoming the effects of radiation than 

 is the simple protection of the thermometer in a j^roperly constructed 

 shelter such as his own. [The actual effect of each has been j)retty 

 thoroughly studied by Ferrel and Hazen.J He recommends urgently 

 the avoidance of large wooden shelters or other masses of wood, as they 

 must retard the temperature changes. 



132. [In 1865-'06 the present writer, while residing at Poulkova Ob- 

 servatory and studying atmospheric refraction, constructed a ther- 

 mometer screen of oiled paper, which is possibly still there, and placed 

 within it bright and black bulb thermometers side by side, adopting as 

 the criterion of excellence of the screen that it must be a perfect pro- 

 tection from outside radiations if these two thermometers read alike, 

 which they in fact generally did. The theorj^ of this method and the 

 formula for correcting the bright bulb in case of any small difference 

 have been lately given by Ferrel in his memoir on temperature. A quite 

 thorough investigation of the merits of various, thermometer shelters 

 and the relative effect of solar, terrestrial, and instrumental radiation 

 and of convection by wind has been recently made by H. A. Hazen, 

 from which it would appear that the Wild shelter (a wooden lattice-work 

 inclosing a sheet-zinc screen with the thermometers inside) does not 

 quite give sufficient ventilation for warm climates; in fact, the meteoi 

 ologist needs the temperature and moisture of the free air, and the 

 criterion of a good shelter must be that the thermometer within gives 

 the same temperature as the thermometer outside, after correcting the 

 hitter for solar and other radiations, the formulae for which have also 

 been given by Ferrel.] In reference to determining the moisture of 

 the air Wild relies largely upon the studies of Sworykin, who found 

 that with a wind of definite and sufficiently high velocity the psychrom- 

 eter, with ventilation, gives verj'^ accurate results as comi)ared with 

 Alluard's dew-point apparatus and Schwackhofer's volume hygrometer. 

 He recognizes the value of the rotation-psychroineter and the sling- 

 psychrometer, but thinks ou account of the time required these meth- 

 ods should only be employed at special stations, and that for ordinary 

 use it is only necessary to add to his own shelter a ventilating appa- 

 ratus fastened to the floor of the shelter, and which is rotated by the 

 hand rapidly just before making an observation ; this draws the air 

 from below up into the shelter and gives the necessary ventilation for 

 both dry and wet thermometers. {Z, 0, Q, M.j xlx, p. 433.) 



