III. MISCELLANEOUS. 11 



through. A tray, divided into compartments, slides beneath the box; it is 

 pushed forward through the space of one compartment before giving a fresh 

 movement to the handle, and thus the seeds become sorted into the different 

 compartments. (This instrument was used to illustrate a lecture before the 

 Royal Institution on Friday evening, February 27, 1874.) 



49. Apparatus affording Physical Illustration of the 

 action of the Law of Error or of Dispersion. 



Francis Gallon, F.R.S. 



Shot are caused to run through a narrow opening among pins fixed in the 

 face of an inclined plane, like teeth in a harrow, so that each time a shot passes 

 between any two pins it is compelled to roll against another pin in the row 

 immediately below, to one side or other of which it must pass, and, as the 

 arrangement is strictly symmetrical, there is an equal chance of either event. 

 The effect of subjecting each shot to this succession of alternative courses is, 

 to disperse the stream of shot during its downward course under conditions 

 identical with those supposed by the hypothesis on which the law of error is 

 commonly founded. Consequently, when the shot have reached the bottom of 

 the tray, where long narrow compartments are arranged .to receive them, the 

 general outline of the mass of shot there collected is always found to assimi- 

 late to the well-known bell-shaped curve, by which the law of error or of 

 dispersion is mathematically expressed. (This arrangement was devised, by 

 the exhibitor, to illustrate a lecture before the Royal Institution on Friday 

 evening, February 27, 1874.) 



50. Practical Approximation to the value of the circum- 

 ference in terms of the diameter, by means of a right angled 

 triangle having one acute angle =27 35' 49'636". 



Edward Bing, Riga. 



For the purpose of effecting this object, as well as for answering 

 kindred questions, use is made of a triangle, specimens of which are* 

 here exhibited, and of which one angle is a right angle and another 

 is defined by an equation. 



