OF PERIODIC PHENOMENA. 351 



restrict our observations to such given points, as 

 may admit of comparison in their results, and re- 

 move the risk of observers labouring to no pur- 

 pose, because not labouring upon any common 

 plan. 



(13.) The meteorological observations which M. 

 Quetelet has proposed should be made, are foreign 

 to the subject of this work. But it may be de- 

 sirable to say more on that part of his scheme 

 which relates to the observing of periodic pheno- 

 mena in Natural History. We may state that, for 

 the guidance of those who may be prevailed upon 

 to join in these inquiries, and to insure a simul- 

 taneity both in their observations and their me- 

 thod of observing, he has published lists of such 

 species of plants and animals as he and others 

 have agreed upon to notice, (and to which it is 

 recommended observers should exclusively confine 

 their attention,) as well as laid down certain con- 

 ditions, which should be strictly kept to, in order to 

 give value to the results. 



(14.) The principal heads of observation are si- 

 milar to some of those we have already presented 

 to the reader in a tabular form (7). They com- 

 prise the times of foliation and defoliation of up- 

 wards of a hundred species of trees and shrubs ; 

 the times of flowering and ripening of the fruit 

 in the same species, and in about two hundred 

 plants besides ; the first appearance and retreat 

 of certain hybernating mammals ; the times of mi- 

 gration of about forty different species of birds, 

 as well as a few other points in their history of 



