The Berlin-Zossen Electric Railway Tests of 1903: A Report of the Test Runs Made on the Berlin-Zossen Railroad in the Months of September to November 1903. E-book. Formato PDF Louis Bell   -  Forgotten Books, 2017  - 

The energy spent in pulling a train over its track may be roughly divided into five elements: work against gravity; work of acceleration; internal resist ance that due to friction within the rolling-stock); external resistances, due to interaction between rolling-stock and track; and air resistance. Of these several items the first two, as such, are pretty definite in character and can be figured in a given case with reasonable precision. The last three are extremely hard to separate and have been the source of many difficulties.

The Telescope. E-book. Formato PDF Louis Bell   -  Forgotten Books, 2017  - 

Much has been written of telescopes, first and last, but it is for the most part scattered through papers in three or four languages, and quite inaccessible to the ordinary reader. For his benefit the references are, so far as is practicable, to English sources, and dimensions are given, regretfully, in English units. Certain branches Of the subject are not here discussed for lack Of space or because there is recent literature at hand to which reference can be made. Such topics are telescopes notable chiefly for their dimensions, and photographic apparatus on which special treatises are available. Celestial photography is a branch Of astronomy which stands on its own feet, and although many telescopes are successfully used for photography through the help of color screens, the photographic telescope proper and its use belongs to a field somewhat apart, requiring a technique quite its own.