MAUPERIN'S INDICATOR. 559 



upon the support ; it is regulated according to the latitude of the place, and 

 the apparatus is then " oriented." 



The upper disc is an elliptical opening, or aperture, which contains for 

 every moment the stars visible upon the horizon, and the circumference is 

 furnished with a graduated scale of hours divided into five-minute divisions, 

 and this is fixed upon the apparatus. The dotted line between the mid- 

 day and midnight points gives the meridian. 



The disc placed underneath is the celestial chart, on the circumference 

 of which we shall find the days of the months. It can be moved around 

 the rod, S, which represents the axis of the earth around which the heavens 

 are supposed to revolve. When the stars have to be observed, the day 

 of the month has to be brought to the time at which the observation is 

 about to be made. We can easily read off the chart by looking through 

 the eye-piece as already explained. Every five minutes it is necessary to 

 move the chart one division, which indicates that five minutes have passed ; 

 (other stars are, of course, arriving). The apparatus can be packed away 

 when done with, or the bearings taken, and then the trouble of getting it 

 into position again need not be repeated. 



A small lamp, L. throws its light upon the chart in such a way that 

 the eyes of the observer are not incommoded, while the table is fully 

 illuminated. It can be placed at L' if necessary. The inclination varies 

 according to the latitude of the place when the observations are made. 

 There is an arrangement underneath which admits of this inclination 

 according to longitude. 



The apparatus can also be made available to ascertain what the aspect 

 of the heavens will be upon any particular evening of the month. We 

 have only to place the chart at the day and hour, and we shall then see 

 upon it all the stars visible above the horizon. We can thus find out at 

 what time the stars rise and set, and those which do not set to find the 

 hour at which they pass the meridian (the line drawn between midday and 

 midnight upon the chart), and the time of their appearance on the horizon. 

 When the sliding indicator, I, does not show a star that is discoverable in the 

 sky, the observer may conclude that he is viewing a planet. This apparatus 

 is well adapted for beginners in astronomy, as no deep preparatory study is 

 necessary, and the tyro can read the sky as easily as he could read a book. 



A COSMOGRAPHICAL CLOCK. 



We have, in the foregoing chapters upon Astronomy, endeavoured to 

 give the reader some idea respecting the inclination of the earth and its 

 rotation, and writers have often endeavoured to devise an apparatus which 

 shall show the position of the globe in space, its diurnal motion even its 

 inclination and the succession of seasons in its revolution round the sun. 

 But such reproductions of simultaneous movements have hitherto been 

 obtained only on a very large scale, which find their place well enough 

 in the museum or lecture-room, but which it is quite impossible to utilize 



