"It will be necessary to explain the spirit of the method of arranging the observed astronomical objects under consideration in such a manner, that one shall assist us to understand the nature and construction of the other. This end I propose to obtain by assorting them into as many classes as will be required to produce the most gradual affinity... and it will be found that those contained in one article, are so closely allied to those in the next, that there is perhaps not so much difference between them... as there would be in an annual description of the human figure were it given from the birth of a child till he comes to be a man in his prime."