16 



SCIENCE. 



[N. S. Vol. II. No. 27. 



The expert topograplier, intuitively, sep- 

 arates minor features of the surrounding 

 terrene from those accidents of the ground 

 which characterize forms that may not only 

 be represented in the scale of the map, but 

 which will also materiallj' assist in deline- 

 ating and representing the general system 

 that may condition such forms. Where the 

 general configuration or surface-modeling 

 conforms to an easily recognizable system, 

 a broader interpretation and a more free 

 treatment of the terrene should be observed 

 than in the case of an area showing diversi- 

 fied forms and having an irregular relief. 



Topographic sketching in this sense not 

 only requires artistic sensibilities, but it 

 also demands a correct and comprehensive 

 interpretation of forms, under a supposition 

 which is at variance with the facts, inas- 

 much as the map is drawn as if the terrene 

 were seen from a point at infinite distance. 



The question now arises : How is the j^oung 

 topographer to be best prepared in order to 

 meet the requirements with general satis- 

 faction ? 



My views fully coincide with those of 

 Professor Davis, given in a recent note in 

 Science, that ' a very careful and sympa- 

 thetic study of the origin of land forms on 

 the ground before the topographer ' will 

 enable him to ' make less mistakes of inter- 

 pretation ' than one whose principal aim is 

 to give mathematically correct locations 

 without possessing any knowledge of either 

 terrene forms or the agencies which pro- 

 duced them. 



Mathematical knowledge in surveying is, 

 of course, a sine qua non, but the studj' of 

 terrestrial relief and the orthogonal projec- 

 tion of the latter into horizontal plan should 

 be made a careful study, and to this the 

 young topographer's attention should be 

 principally directed, guarding him, however, 

 against falling into that error wliich a 

 thorough familiaritj' with structural geology 

 and a knowledge of its originating; causes are 



apt to commit, namely, never to represent 

 on the chart imaginarj^ forms of topograph- 

 ical elements that are not visible from the 

 occupied stations in the field. In other 

 words, the topographer should not, on the 

 strength of a familiaritj' with structural 

 geology, attempt to sketch the contours on 

 the further (invisible) slopes of hills merely 

 by inference, or, because the contours de- 

 lineating the visible slopes before his eyes 

 maybe well determined, and, in a measure, 

 may suggest the probable shape of the 

 further sides. 



I believe with Professor Davis, that " the 

 best course of education for topographers, 

 while yet in school, should include a careful 

 study of the development of land forms," 

 which may be done in various ways. 



A ' comparative ' studj' of relief-models 

 with two sets of topographic maps (all on a 

 large scale) of the same area — one set with 

 hill-shading and the other with horizontal 

 equidistant contours — together with a series 

 of panoramic views, covering the same area 

 and taken with a surveying camera, would 

 probably give the student not only excellent 

 means for comparing the ' representative 

 force ' of the various conventional methods 

 of indicating topographic forms, but an in- 

 telligent comparison of the maps and model 

 with the photographs (or with nature) 

 would train the young topographer into see- 

 ing the facts, and he would thus make a 

 good start towards acquiring facility in 

 sketching topographic forms of the terrene 

 spread out before him. 



A course of ' iconometric ' platting, on a 

 large scale, from photographic perspectives 

 (metro-photograph J'), would also offer an 

 excellent opportunity, not only to demon- 

 strate how the elements selected as char- 

 acteristic points in the landscape are inter- 

 preted or transposed into horizontal plan, 

 but such a course would also offer the stu- 

 dent the means to clear anj' doubt he may 

 have regarding the transposed forms of 



