DR L. BECKER ON THE SOLAR SPECTRUM. 103 



the end of a half-inch steel rod 12 inches in length, the other end carries a 12^-inch gun- 

 metal wheel (B) with 150 teeth. The position of the rod can be adjusted to insure 

 proper contact of the screw with the worm-wheel. A system of wheelwork turns 

 the wheel B. The latter is geared into a If -inch pinion (b) of 15 teeth, on the axis of 

 which a second wheel (C) of 11^ inches diameter and 140 teeth gears with a second pinion 

 (c) of the same dimensions as the first. The two horizontal axes of b, C, and c are 

 clamped in the slot of an adjustable bracket. All these appliances are attached to a 

 strong mahogany frame, 2 feet square by 2 feet high, provided with three foot screws, 

 and carried by a massive concrete pier. 



It is apparent that the angular motion of the second pinion (c) is 180 x ^-^ x 1 1 ^ ) 

 equal to 16,800 times as large as that of the grating. By a long f-inch iron rod the 

 second pinion can be turned by the observer from the eye-end of the viewing telescope. 



The rod, however, is not fixed immediately to the pinion, but transmits its angular 

 motion by a very useful kind of joint, without communicating any longitudinal vibration. 

 It is employed by Mr L. Casella in his recording anemometers, and was introduced here 

 at the suggestion of Dr Copeland. Two square bars are screwed crosswise together, each 

 of which fits exactly without tightness into a deep groove in a corresponding disk. The 

 grooved surfaces of the disks face each other, and turn in parallel planes, the only con- 

 nection between them being the gliding cross. If the axes of rotation be parallel, 

 although not necessarily in the same line, the transmission of rotary motion from one to 

 the other is perfect. To prevent the cross from altering its plane of rotation, one of its 

 bars has a projecting plate which slides in narrow channels at the back of the groove of 

 the corresponding disk. In our instrument one of the disks is carried by the second 

 pinion (c), while the axis of the other is supported by the pillar of the viewing telescope, 

 and is connected with the long iron rod by a Hooke's joint. 



Underneath the eye-end of the viewing telescope, the other end of the iron bar is 

 attached, by another Hooke's joint, to the axis of a wooden " recording " wheel. This 

 wheel, which is 6^ inches in diameter, rotates inside a narrow box in such a way that 

 its rim, 2 inches in breadth, is level with the outside of the lid of the box. Above the 

 exposed part of the recording wheel is a loaded swing frame carrying a roller of the full 

 breadth of the wheel. Both wheel and roller are covered with sand paper, to insure a 

 grip on the paper fillet which passes between them. A load of about 5 lbs. is sufficient 

 to prevent slipping. When observing, it is by turning this roller that the grating is 

 moved. The paper, 1-| inch wide, is supplied from a large roll inside the box, and passes 

 through a slit in the lid and over a flat surface to the wheels. On the lid, turning on a 

 common axis, are five recording levers provided with prickers at their free ends. The 

 prickers, which form dots in a straight line across the fillet about f inch apart, are easily 

 worked by the thumb and fingers of one hand, either singly or simultaneously. To this 

 end the levers are suitably splayed at the fulcrum ends. The levers are smartly raised 

 by springs as soon as the pressure is removed. Thirty-one different records can be made 

 by the various combinations of the five needles, but only 19 have been employed. The 



