THE CLASSIFICATION OF THE SCIENCES 517 



writers on various branches of engineering practice. It is 

 termed Descriptive Geometry, or the Geometry of Position, 

 and a branch of it, probably familiar to the reader, is 

 Perspective Geometry. On the quantitative or measuring 

 side of the special space division of Abstract Science, we 

 deal with size, and find such subdivisions as Metrical 

 Geometry — of which a large part of Euclid's Elements is 

 constituted, — Trigonometry and Mensuration. 



The second branch of special relations ought to deal 

 with Time, but as in reality all our spacial discrimination 

 is associated with time, so all our temporal discrimination 

 is associated with space ; we do in actual perception 

 separate all things in both time and space concurrently, 

 for the immediate groups of sense-impressions are not 

 really simultaneous, and most things perceived in space 

 are "constructs" involving stored sense-impresses (pp. 42, 

 183). When, therefore, we speak of the special re- 

 lations of Time, we are referring to that discrimination 

 by sequence which we term change, and of which the 

 fundamental element is really the time-mode of perception 

 — conceptually we are referring to change as measured in 

 Absolute Time (pp. 189, 241). When changes are not 

 measured quantitatively, but only described qualitatively, 

 we require a theory by aid of which we may accurately 

 observe and describe such changes. We want not only a 

 scientific theory of measurement, but a scientific theory of 

 observation and description. For example, in the case of 

 organic phenomena of all sorts it requires a scientific train- 

 ing not only to know what it is essential to observe, but 

 how what has been observed should be described. Some 

 discussion of the Theories of Observation and Description 

 are given in treatises on Logic, but they seem capable of 

 much more complete treatment than they have at present 

 received.^ 



The last branch of Abstract Science to which we must 

 refer is the quantitative side of change. Thus we may 



1 One of the best practical trainings in Obso-vation and Description is that 

 to be obtained by a clinical clerk in a hospital ward. Another good training, 

 I have noticed, is almost unconsciously acquired by the careful sketcher or 

 painter of flowers and trees. 



