ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



579 



(3) Illuminating' and other Apparatus. 



An Easily Set-up Heliostat.* — A. W. Gray has contrived a helio- 

 stat (Fig. 82) oat of simple materials. He uses a framework in the shape 

 of a right-angled triangle, the vertical side being applied to the window 

 of the room, and the base resting on the window-sill : means are provided 

 for fixing. The hypotenuse of the frame must be inclined to the base 

 at an angle equal to the geographical latitude of the place. By help of 



Pig. 82. 



a bracket at right angles to the hypotenuse the mirror axis (made out 

 of a bicycle pedal) is arranged parallel to the hypotenuse. One ex- 

 tremity of this axis bears a plane mirror, which reflects the sunlight 

 upwards on to another plane fixed mirror, which, again, reflects it 

 horizontally into the room. In order to secure the rotation of the 

 lower mirror, the axis above mentioned is connected at its lower end 



*|Dentsche Mechaniker-Zeit., ii. (June 1, 1904) p. 104 (fig.); Zcitschr f. A. 

 plij r 8. u. Chein. Unterr. xvii. (1904) p. 25. 



