while for structures located in the street it varies from forty-seven to fifty-three feet according to the transverse distance between vertical axes of columns, the greater the distance the greater the economic span length. With heavier live loads the economic span lengths would be shorter.

FOUR-COLUMN VERSUS TWO-COLUMN STRUCTURES.

In four-track structures located on private property there is but little, if any, difference in the cost whether four columns or two columns per bent be employed; but preference is given to the former on account of rigidity.

BRACED TOWERS VERSUS SOLITARY COLUMNS.

In structures on private property there is quite a gain in both rigidity and economy by adopting braced towers spaced about one hundred and fifty feet centres.

RAILS.

The author prefers to adopt for elevated railroads steel rails five inches high weighing not less than eighty pounds to the yard, so as to provide for the excessive wear caused by the constantly passing trains.

TREATED VERSUS UNTREATED TIMBER.

Extended investigations have proved to the author's satisfaction that it pays well to preserve the track timber, and that, up to the present time, by far the best preservative process is vulcanizing.

PEDESTAL-CAPS.

The most satisfactory and economical pedestal-caps are of concrete covered with at least six inches of first-class granit-