and sand or coarse gravel will sustain any reasonable weight without danger of yielding.
Little needs to be added upon adhesion. Many attempts have been made to determine the adhesive strength of various cements, usually without success—not because they do not hold properly, but because they hold until the brick or stone to which they have been applied is ruptured before the cement is separated from its surface. This shows that the adhesion is always sufficient for all uses, and this seems to be true of all our native cements. Their use, therefore, mixed with mortar adds greatly to the strength of the structure.
All these qualities of cement warrant its continual and increased use, particularly of all the better grades. Probably the English Portland is the best of all, but its cost is so much beyond that of our native cements as to warrant using them in its place in somewhat larger proportion in all places where time can be allowed for the hardening.
| SKETCH OF THEODOR SCHWANN. |
By M. LÉON FRÉDÉRICQ.
ON the 23d of January, 1878, was celebrated at the University of Liége, by the scientific men of Belgium and others representing neighboring European states and more distant countries, the fortieth anniversary of the professorship of Theodor Schwann. Men of all nations joined, by their presence or by letter, in honoring the man who, as the founder of the cell theory, had showed that all the varied and complex manifestations of Nature are one in kind, and had given a new direction to physiological research.
The object of this demonstration, Theodor Schwann, was born on the 7th of December, 1810, at Neuss, near Düsseldorff, in Rhenish Prussia, and died in Liége, in January, 1882. His father and grandfather were goldsmiths; but the father, after Theodor was born, established a printing-office—himself, with the aid of an artisan, constructing the first press—which has become one of the most prosperous concerns of the kind in the Rhenish country. From it was issued the memorial volume published in 1879 in honor of Theodor Schwann.
The youth inherited from his father a decided taste for manual occupations, which afterward proved of great assistance to him in his laboratory work. While still a child he used to spend his play-hours in making miniature instruments of physics with the most primitive materials. From the primary school he went into
