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POPULAR SCIENCE MONTHLY. 



that this, including the calculus and differ- 

 ential equations, can not be safely neglected 

 by the engineer though some of the more 

 abstruse portions of the subject might be 

 dispensed with. Physics is of great impor- 

 tance, for there are few problems in engi- 

 neering in which no part is borne by phys- 

 ical considerations. The surveyor avails him- 

 self of physics when heights are measured 

 by the barometer, or by the temperature at 

 which water boils. Evaporation, condensa- 

 tion, and latent heat bear upon the efficiency 

 of steam engines, and the expansive force 

 of gases, the retention of the heat devel- 

 oped, and the diminution of friction on the 

 economical working of heat engines. Con- 

 siderations of temperature limit the height 

 to which railways can be carried without 

 danger of blocking by snow, and the depth 

 at which tunnels can be driven. Compressed 

 air is largely used by engineers. Electric 

 engineering, too, is intimately connected with 

 physics. Chemistry is of importance in the 

 manufacture of iron, steel, and other metals, 

 and the formation of alloys, and in its relation 

 to explosives. A knowledge of geology is 

 indispensable in directing a search for coal, 

 iron ore, and the metals, and in the execu- 

 tion of all works going below the surface. 

 Meteorology is useful to the engineer in that 

 it enables him to know the force of the wind 

 and the direction, duration, and periods of 

 occurrence of severe gales very important 

 matters in the construction of bridges and 

 harbor works. 



A Valley of White Limestone. A re- 

 markable formation is described by Mr. 

 Theodore Bent as observed by him while ex- 

 ploring the frankincense country of Arabia, 

 near the presumed site of the Abyssapolis 

 of Ptolemy. The valley leading down to the 

 Red Sea has been filled in the course of 

 ages by a calcareous deposit, which is col- 

 lected on either side of an isolated hill in 

 the middle of the hollow, about one thousand 

 feet in height. This deposit has taken the 

 form of a straight and precipitous wall five 

 hundred and fifty feet high and three quar- 

 ters of a mile long on the eastern side of the 

 hill, and about a quarter of a mile long and 

 three hundred feet high on the western side. 

 Over these walls feathery waterfalls pre- 

 cipitate themselves, adding perpetually to 



the chalky accretions of which the cliffs are 

 constructed. The general appearance of the 

 walls is white and whitish gray, with long, 

 white stalactites hanging down in tumbled 

 confusion. They are streaked here and 

 there, where the water perpetually falls, 

 with patches of green. Beneath plateaus 

 twenty feet high enormous ricinuses, da- 

 turas, and other plants flourish ; and the 

 Bedouins have utilized the stream before it 

 has lost itself in the rocky channel to make 

 small gardens. The rocky channel below is 

 also very curious, presenting a flat surface 

 a^out fifty yards across of white calcareous 

 rocks, while just below the wall where the 

 water comes down is an enormous amount 

 of white calcareous deposit, soft and spongy 

 to walk upon. Mr. Bent pronounces this 

 one of the most stupendous natural phe- 

 nomena he has ever seen, characterizes the 

 valley as "a stupendous abyss," and com- 

 pares the whole with the pink and white ter- 

 races of New Zealand and the calcareous 

 deposits of Yellowstone Park. 



Geology and Paleontology at Union 

 University. The department of Geology 

 and Paleontology of Union University offers 

 the ordinary course of the college and spe- 

 cial courses for such students as are inter- 

 ested in the science from a philosophical or 

 professional point of view. The courses in- 

 clude mineralogy and lithology, general geol- 

 ogy (with excursions), economic geology, in 

 which are considered in the second half the 

 occurrence and distribution of the mineral 

 deposits and building stones of the United 

 States ; systematic and structural geology 

 and paleontology, with especial considera- 

 tion of the formations occurring in New 

 York and adjacent States and their char- 

 acteristic fossils ; field and laboratory study 

 of the geological formations readily acces- 

 sible from Schenectady ; the methods of 

 preparing geological maps and reports ; and 

 advanced field work and independent re- 

 search, in which the student selects some 

 region for original work to which he can de- 

 vote considerable time, and conducts his in- 

 vestigation in a professional manner. He is 

 expected in this to demonstrate his ability 

 to conduct original work, and to prepare a 

 report containing a summary of the previous 

 knowledge of the geology of the region, with 



