460 THE POPULAR SCIENCE MONTHLY. 



In addition to the concave mirror, each magnet carries a plane 

 mirror to receive the reflection of a scale attached to the back of a 

 small telescope. The telescopes are mounted upon the stands of the 

 recording instruments, and for convenience of observation are pro- 

 vided with diagonal eye-pieces. On looking into either telescope one 

 sees its scale reflected in the plane mirror carried by one of the mag- 

 nets. When the mirror turns with the swing of the magnet, the scale 

 appears to the observer to traverse the mirror's face. At the begin- 

 ning and again at the end of each trace a record is made of the divis- 

 ion of the scale then covered by the cross-wires of the telescope. 

 Knowing the times at which each trace was started and stopped, and 

 the readings of the scale at those times, it is easy to divide off the paper 

 into spaces corresponding to the hours of the day and into other spaces 

 at right angles to these corresponding to divisions of the scale. An 

 exact record is thus made of all magnetic variations. 



Particular interest attaches to magnetic observations on account 

 of the way in which the magnetic state of the earth seems to be influ- 

 enced by the position of the sun, and to a slight degree by the posi- 

 tion of the moon; also from the connection between auroral displays 

 and magnetic variations, curves representing the frequency of either 

 agreeing quite closely with curves representing the area of the sun 

 covered by spots. It is well to remark that the curves representing 

 magnetic variations and auroras lag about six months behind those 

 representing the sun-spot variations. The sun-spot area seems in 

 some way to depend upon the position of the planets. Not only is 

 the earth's magnetism thus, seemingly at least, influenced by the sun- 

 spots, but also some of the phenomena of the weather. These last are, 

 of course, in general, masked by local disturbances ; but, lately, a very 

 remarkable agreement has been shown to exist between certain mag- 

 netic and barometric traces. Investigations into the causes of mag- 

 netic variations and the laws under which these variations occur are 

 made by officers of the United States Coast Survey ; and to the head- 

 quarters of this survey, at Washington, are forwarded, each month, 

 the traces obtained at Madison. 



--- 



THE CHEMISTRY OF FRUIT-RIPENING. 1 



By ALBEET B. PEESCOTT, 



PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF MICHIGAN. 



TO form the seed seems to be the chief end of the plant, When 

 in the vigor of its own maturity, and when receiving the sun's 

 strongest rays and the earth's richest nourishment, the plant gathers 



'From the forthcoming "Transactions of the, Michigan Pomological Society" for 

 1877 ; furnished by the author for The Popular Science Monthly. 



