130 ANNUAL OF SCIENTIFIC DISCOVERY. 



THE CLOUD-MIRROR AND SUNSHINE-RECORDER. 



At the meeting of the British Association, 1SG1, Mr. J. T. Goddard 

 called attention to the two above-named contrivances. The cloud- 

 mirror was simply a mirror of a circular form with the points of the 

 compass marked on its frame ; this, being presented face upwards to 

 the sky, enabled a person to draw with considerable accuracy, at any 

 desirable moment, the configuration of the clouds relatively to the 

 horizon and to each other. The sunshine-recorder was a piece of 

 photographic paper placed in the bottom of a box blackened inside, 

 the top of which had in the centre a small circular hole, through 

 which a slender beam of sunlight could be admitted to pass on to the 

 photographic paper. When the sun did not shine no mark was left 

 on the paper ; when it did, its varying diurnal course left a corres- 

 ponding line on the paper, its position marking the hours of sunshine, 

 and its breadth and depth of shade indicating the greater or less radi- 

 ating power of the sun. 



The President observed that he had once been shown a very 

 simple sunshine-recorder. It consisted merely of a hollow hem- 

 ispherical wooden disk, concentric with which was placed a glass 

 spheric lens, whose focal length was made exactly equal to the radius 

 of the wooden disk. As the sun moved along in its diurnal course, 

 the concentrated light and heat burned a corresponding line on the 

 bottom of the disk, more or less intense the brighter or less brightly 

 it radiated, and altogether deficient when it was obscured by clouds. 



THE TROCHEIDOSCOPE. 



This name has been given to a recent invention designed for dis- 

 playing various effects of the combination of colors upon a novel 

 principle some of them in a most brilliant manner. It consists 

 mainly of a train of wheelwork, so arranged that by gently turning 

 the handle the horizontal disk-table is made to revolve at varying 

 speed, at the will of the operator, from fifty to two thousand revolu- 

 tions per minute. In the centre of the disk-table is a carefully-fitted 

 spindle, with a screw and flange at the lower end, and a shoulder at 

 the upper end, just under which is a universal joint for adjusting the 

 position of the topmost portion, upon which the patterns or devices 

 are to be hung when exhibited. Proceeding from the side of the 

 instrument is an arm of brass, with a small appendage or hook at the 

 top for receiving the strings of the patterns, and a spring to act as a 

 check upon the disks used in the protean experiments. The spindle 

 is jointed near the top to give a peculiar vibratory motion to the pat- 

 tern when fitted. As the spindle revolves it strikes the sides of the 

 circular hole by which the pattern is suspended, and so imparts to it 

 a shaking motion just sufficient to fill up the pattern with all the colors 

 on the disk below, but then lost to the eye by its rapid revolutions. 

 If the pattern were perfectly still, the colors would not appear ; but 

 if allowed slight motion, as above described, the colors are reproduced 

 upon the principle that of images being retained upon the eye 

 which is thus elucidated in a very beautiful manner. Described and 

 figured in the London Mechanics' Magazine. 



