SKETCH OF THE ODOR SCHWANN. 257 



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 in- 

 creased use, particularly of all the better grades. Probably the 

 English Portland is the best of all, but its cost is so much be- 

 yond 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. LEON FREDERICQ. 



ON the 23d of January, 1878, was celebrated at the University 

 of Lie'ge, by the scientific men of Belgium and others rep- 

 resenting neighboring European states and more distant coun- 

 tries, 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 physio- 

 logical research. 



The object of this demonstration, Theodor Schwann, was 

 born on the 7th of December, 1810, at Neuss, near Dusseldorff, in 

 Rhenish Prussia, and died in Lie'ge, 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 



VOL. XXXVII. — 20 



