OF ARTS AND SCIENCES: JANUARY 9, 1872. 343 



Professor E. C. Pickering exhibited a new form of dividing 

 engine in which the scale to be engraved is moved forward equal 

 amounts at each stroke, the distance being regulated by a pin 

 moving between a plate of brass and the end of a screw. In 

 this instrument, as there are no joints, this source of inaccuracy 

 is avoided, and it is also free from the usual errors of a mi- 

 crometer screw. The model shown, although made of pine- 

 wood, gave results approaching in accuracy those of the best 

 metal dividing engines. 



Professor N. S. Shaler made a communication on the con- 

 nection between the development of the life and the physical 

 conditions of the several continents. 



It has been shown that the several continents vary in the extent to 

 which their shore line is irregular. If we arrange the several conti- 

 nents according to the amount of shore line compared with the internal 

 area, we get a series in which they stand in the following order : 

 Europe, North America, South America, Australia, Asia, Africa ; 

 but if we represent the continents in such a fashion that all have the 

 same area, retaining for each the general outline which it now has, 

 then we obtain a series in which Australia has the least shore in pro- 

 portion to area, South America next, Africa and Asia next and approx- 

 imately equal, North America next, and Europe the highest in the 

 series, having several times as much shore line as Australia and much 

 more than North America. It will be evident, on consideration, that 

 this analysis enables us roughly to compare the conditions of surface on 

 the several land masses. Those which have the largest amount of shore 

 line in relation to area are those which have the most diversified sur- 

 faces, and conversely. With this series let us compare another series 

 derived from the development of life on these continents. If we take 

 these continents and tabulate their organic life, in so far as is necessary 

 to determine the number of ancient types surviving on each, we may 

 construct another series. It is true that this will be only approximative, 

 but it will indicate the relative zoological inferiority of any continent, 

 so far as we can infer that from the survival there of types of organic life 

 which have disappeared from the others. This second series will cor- 

 respond with the first, the continents being inferior as a whole in their 

 organic development in proportion to the relative shortness of their 

 shore lines : or, in other words, to the want of variety of their surfaces. 



