161 



All these data for different ages were expressed by projection 

 npon ruled paper, and interpolating curves used to deduce the mean 

 results, which were then tabulated. A comparison was instituted 

 with M. Quetelet's conclusions, from experiments on a similar class 

 of individuals in Belgium. Tlie following deductions were made : 



1. That, in respect of weight, height, and strength, there is a 

 general coincidence in the form of the curves with those of M. 

 Quetelet. 



2. In Britain, the progress towards maturity seems greater in 

 the earlier years (14 to 17) than in Belgium, and slower after- 

 wards. This seems more strongly indicated in the English than in 

 the Scotch curves. 



3. The superior physical development of natives of this country 

 above the Belgians is very marked. In strength it is greatest (^th 

 of the ivhole) ; in height least. 



4. So far as the English and Irish curves can be considered as 

 correct, they indicate that the English are the least developed of 

 the natives of Britain at a given age, the Irish most, the Scotch 

 retaining an intermediate place. 



5. The maximum height is barely attained at the age of 25. 



6. All the developments increase during the period of observa- 

 tion (14 to 26 years of age), and all increase more slowly as age 

 increases. Hence the curves are all convex upwards, (the abscissse 

 or ages being projected horizontally). 



3. Description of a Single Achromatic Eye-Glass. By Ed- 

 ward Sang, Esq. 



The author observes that, " in combining the surfaces of an 

 achromatic eye-piece, a very limited question is resolved. The 

 condition is, that pencils of light falling upon the first surface in 

 directions parallel [approximately] to the axis of the instrument, 

 emerge from the last surface in such a way, that the different rays 

 into which each is decomposed may be parallel among themselves. 

 On account of this restriction, achromatism can be obtained by the 

 use of only one medium, and it is unnecessary to combine sub- 

 stances acting differently on the light of various colours." 



The author then proceeds to show that, since the only required 

 conditions are that two refiractions shall take place of a certain 

 amount and at certain distances, these conditions may be fulfilled 



