Kansas Academy of Science. 53 



NOTE ON A DEVICE FOR SETTING A HELIOSTAT IN 

 THE MERIDIAN. 



Edison Pettit. 



THE DEVICE is based on the principle of Burt's solar 

 compass. On the side of the fork carrying the revolving 

 mirror is placed an arm carrying at one end a pinhole in a 

 disk, and at the other a screen with a cross mark for receiving 

 the image of the sun cast by the pinhole. This arm carries an 

 arc graduated in 24 degree marks on either side of the line 

 joining the pinhole and the cross, and works against a vernier 

 arc. When this arm is perpendicular to the fork the vernier 

 reads zero. The mirror is provided with a graduated arc 

 which reads zero when the mirror makes an angle of 45° with 

 the polar axis, and is graduated into 24 half-degree divisions 

 on either side of the degree mark. 



The operation of setting the instrument is as follows: The 

 mirror arc and solar compass are both set to read the declina- 

 tion of the sun. Then by revolving the mirror fork about the 

 polar axis and the whole instrument about the vertical axis, 

 the image cast by the sun may be brought to fall on Ihe cross. 

 The mirror and vertical axis are then clamped and the clock 

 started. The instrument is now in the meridian and will carry 

 the beam of light indefinitely. An instrument constructed on 

 this plan several years ago has demonstrated the convenience 

 of the solar compass. A complete description of this apparatus 

 and theory will be found in Popular Astronomy, vol. XXI, 

 No. 9. 



Washburn College Observatory, Topeka. 



