P OP ULAR MIS CELL ANY. 



59 



had rooms in the Cooper Union Building, 

 but from the beginning it has been the in- 

 tention of the leading members to secure 

 possession of a building large enough to re- 

 ceive their valuable collection and library. 

 The new headquarters is a large four-story 

 and basement brown-stone front house on 

 Twenty- ninth Street, near Fifth Avenue. On 

 the first floor is a spacious reception-room, 

 extending the entire depth of the house ; its 

 walls are covered with maps and charts. 

 One of the curiosities of this room is the 

 large map of South America once used by 

 Humboldt. On this floor is also the room 

 of the president of the Society. The second 

 floor is devoted to the library and the sec- 

 retary's room. Iu the library are 20,000 

 volumes, classified according to countries. 

 The third floor contains the collection of 

 maps and atlases. On the fourth floor is 

 the Council's room, and in the basement 

 are the offices for the clerical force. 



On the evening of November 29th a sec- 

 ond reception was held by the Society, and 

 a paper on a journey to the Spitzbergen 

 Sea was read by A. H. v. d. Hoeck. The 

 author took occasion to expatiate upon the 

 value of arctic research, pointing out the 

 important results thence to be derived for 

 anthropology, zoology, geology and paleon- 

 tology, physics, and meteorology. Manuel 

 M. Pereira, minister resident of Costa Rica, 

 read a short paper on the projected canal 

 across the Isthmus of Darien. 



Hygrometers. An hygrometer is an in- 

 strument for measuring the moisture of the 

 atmosphere. It is often useful for gauging 

 the dryness of rooms. It may not be gen- 

 erally known how simply such an instru- 

 ment may be constructed. 



When water, by means of a moist rag 

 (whose moisture may be kept up by contact 

 with water in a saucer or teacup), is spread 

 over the surface of the bulb of a thermom- 

 eter, the mercury in the latter falls, generally 

 several degrees. The reason is, that the 

 water evaporates and cools the bulb. The 

 evaporation which takes place is, of course, 

 produced by the absorption of heat from 

 surrounding objects, the bulb included. The 

 thermometer is affectsd in proportion to the 

 reduction of temperature caused by the 

 evaporation. It is evident that just as much 



heat as is required to convert water into va- 

 por, just so much cold (or deprivation of 

 heat) will be required to convert the vapor 

 back again into water. When vapor begins 

 to condense into water the temperature is 

 at what is called the dew-point. It is evi- 

 dent, therefore, that theoretically the dew- 

 point is twice as far as the vapor-point be- 

 low the normal temperature of the atmos- 

 phere. Experiments show that it is a lit- 

 tle more; a constant quantity of 1| Fahr. 

 having to be added for heat lost and dissi- 

 pated in the process. 



These facts may be exemplified as fol- 

 lows : Hang two thermometers in a room of 

 equable temperature, and suspend a third 

 in a tin or glass vessel containing some 

 tepid water. Wet the bulb of thermometer 

 No. 2 as suggested above, and the evapora- 

 tion will show the vapor-point. Pour ice- 

 water gradually and slowly into the vessel 

 containing No. 3, and mingle it well with 

 the water already there until the whole be- 

 comes so cold that the exterior of the ves- 

 sel begins to contract moisture. It is then 

 at the dew-point, and the thermometer in 

 the vessel will be found to have fallen twice 

 as much as No. 2, and l{j- more. 



No. 2 is a perfect hygrometer, as it 

 shows the relative dampness of the atmos- 

 phere. When the latter is very dry, as in a 

 room warmed by a hot-air furnace, evapo- 

 ration takes place rapidly, and a large quan- 

 tity of heat is abstracted from the bulb. 

 When moist, as during a shower, very little 

 evaporation takes place, and there is but a 

 slight fall of the hygrometer. When the at- 

 mosphere is too dry the lungs suffer. It 

 is in a wholesome condition when the hy- 

 grometer does not fall more than 7 Fahr. 

 below the normal temperature. A hot-air 

 furnace often sends it down 10 or 12 be- 

 low. 



The Studies of an Engineer. Prof. Rey- 

 nolds, of Owens College, Manchester, in an 

 address on " Engineering as a Profession," 

 proposes the following course of prepara- 

 tion for the student who aims to be an en- 

 gineer : Up to the age of sixtean or seven- 

 teen he should devote himself to acquiring 

 a " general education." Then he enters on 

 his special course. In this he must learn 

 something of science and something of art ; 



