that, as a whole, the engineering profession indorses the statement. The only ordinary cases where multiple systems are employed nowadays are those of the lattice girder and the Whipple truss. The former is conceded by the leading bridge-designers to be unscientific, clumsy, often unsightly, and always uneconomical; and as for the latter, there is no longer any excuse for its use, because it has been ousted from the position it used to hold by the Petit truss, which excels it in every particular, including appearance, economy of material, and mathematical correctness.

Principle XV.

The employment of a redundant member in a truss or girder is never allowable under any circumstances, unless it be in the mid-panel of a span having an odd number of panels, in which case, for the sake of appearance, two stiff diagonals can be used.

The reason for this is perfectly clear when one considers that it takes extra metal to build the said redundant member, and that its use upsets the calculations of stresses, rendering them in fact insolvable. A lengthy treatise was published a few years ago in India upon a method of finding stresses in redundant members, in which much good mental energy was wasted, for the entire book might have been written in these four words: "Never use such members." It is not often that an American engineer is found guilty of employing unnecessary pieces in his designs, but one cannot say the same of his European brethren.

Principle XVI.

The use of a curved strut or tie in bridge-designing for the sake of appearance (or for any other reason) is an abomination that cannot for an instant be tolerated by a good designer.

 It is hardly necessary to make such a forcible remark as this to American engineers,  although in travelling about the United States one occasionally runs across a violation of the self-