114 Notice of some Recent 



until the clapper was loosened, when the mercury rose and 

 continued to undergo a kind of starting, every time that the 

 clapper struck the bell. Mr. Pigott observed the height 

 of the mercury, during the sounding, 29*469. Sir H. Engle- 

 field found its maximum height 29*480, minimum 29*474 ; 

 maximum 29*482, minimum 29.472. Hence, the effect of 

 sound upon the barometer extends to the -^Vo ano ^ To"oo"o 

 of an inch.* It is remarkable, that Pigott generally made 

 the height 3-0V0 ^ ess tnan Englefield. The latter attributes 

 such discordances to the difference in the eyesight. 



II. OPTICS. 



1. Stroboscojie. — Stampfer has invented some interesting 

 stroboscopical tables, or glasses, founded upon a similar 

 principle with the traumatoscopical figures. The first idea 

 of this instrument originated with Plateau. He termed it 

 phenakisticope.-f- By turning a wheel, figures are seen to 

 walk, jump, pump water, &c. The table, or plate, is cir- 

 cular, and moves round on its centre. The actions consist 

 of 8 or 10 postures. If it is wished to represent a man 

 bowing, the first position is, a man standing straight ; in 

 the second, he has a slight inclination ; in the third, still 

 more ; and so on to the sixth position, where he has the 

 greatest flexure ; the four following represent the figure 

 recovering its straight posture, so that the fifth and seventh, 

 the fourth and eighth, the third and ninth, the second and 

 tenth figures have the same posture. Between each of the 

 figures on the periphery of the plate, there is a slit -J inch 

 long, and \ inch wide, in a direction parallel with the radii 

 of the plate, and extending to an equal distance from the 

 centre. If the image is placed before a mirror, and the 

 plate is made to swing round on its centre, while we look 

 through the apertures held before the eye, we shall observe 

 in the mirror, the figures bowing continually, and with a 

 rapidity proportionate to the rate at which the plate turns 

 round. The illusion depends on the circumstance, that the 

 plate between each aperture is covered, while the figure 

 goes farther. That the deception may be complete, it is 



* Young's Lectures, ii. 269. 



t Correspond. Math, et Phys. de PObaarvatorie de Bruxelles, June, 1833. 

 .lahresbericht, 1834, 22. 



