Passing to another point of the same subject, Professor Riedler considers the best dimensions that should be given to the mains.  Resistance decreases with an increase in the diameter of these and in direct ratio to their diameter; for this reason—­still assuming a pressure corresponding to a velocity of 20 ft. per second—­with a fall of one atmosphere, a length of 40 kilometers could be succesfully worked.

The mains of the new reseau for the Quai de la Gare station are 19.69 in. in diameter; they are built up of steel plates riveted, and this Professor Riedler considers to have been a serious error on account of the extra resistance offered by the large number of rivet heads.

The following may be taken as a brief summary of Professor Riedler’s conclusions:  Recent improvements in central station practice have resulted in an increased efficiency of about 30 per cent. in the compressors, but this benefit can only be realized when the new station is in operation.  That the small and very imperfect air engines in use on the system give an efficiency of 50 per cent., while with ordinary steam engines driven by air an efficiency of 80 per cent. can be reached with a very small expenditure of fuel for heating the air before admitting it into the motor.  That special attention should be given to the improvement of air engines, and that with increased initial pressures at the central station the distance of the transmission can be very considerably augmented.  Finally, Professor Riedler claims that power can be transmitted by compressed air more conveniently and more economically than by any other means.

* * * * *

[Continued from SUPPLEMENT, No. 802, page 12810.]

THE BUILDERS OF THE STEAM ENGINE—­THE FOUNDERS OF MODERN INDUSTRIES AND NATIONS.[1]

[Footnote 1:  An address delivered at the Centennial Celebration of the American Patent System, Washington, April, 1891.]

By Dr. R.H.  THURSTON, Director of Sibley College, Cornell University.

Papin, Worcester, Savery, were the authors of the period of application of the power of steam to useful work in our later days.  The world was, in their time, just waking into a new life under the stimulus of a new freedom that, from the time of Shakespeare, of Newton, and of Gilbert, the physicist, has steadily become wider, higher, and more fruitful year by year.  All the modern sciences and all the modern arts had their reawakening with the seventeenth century.  Every aspect of freedom for humanity came into view in those days of a new birth.  Both the possibility of the introduction of new sciences and of new arts and the power of utilizing all new intellectual and physical forces came together.  The steam engine could not earlier have taken form, and, taking form, it could not have promoted the advance of civilization in the earlier centuries.  The invention becoming possible of development and application, the promotion of the arts and of all forms of human activity became a possible consequence of its final successful introduction into the rude arts that it was to so effectively promote and improve.