magnetism, magnetic interference, etc. He has been able to trace out the direction of the lines of force produced in the liquid with the apparatus represented in Fig. 2. A light sphere or cylinder is mounted in the midst of the liquid upon an elastic rod, so that it shall partake of every movement of the surrounding water; a brush is attached to it, and arranged in such a manner as to paint, on the glass plate above, the line of every vibration of the fluid important enough to move it. If two drums are used pulsating concordantly, a figure is obtained precisely like that produced by iron filings in a field of two similar magnetic poles. If the pulsations are discordant, the figure is like that obtained with two dissimilar poles. Three pulsating drums give a figure identical with that produced by three magnetic poles.
A number of interesting conclusions may be drawn from these experiments concerning the nature of electric and magnetic vibrations, but they need to be further confirmed before a positive announcement of them can be justified.
| THE CAUSE OF TUBERCULAR DISEASE. |
LETTER FROM PROFESSOR TYNDALL TO THE LONDON "TIMES."
ON the 24th of March, 1882, an address of very serious public import was delivered by Dr. Koch before the Physiological Society of Berlin. It touches a question in which we are all at present interested—that of experimental physiology—and I may, therefore, be permitted to give some account of it in the "Times." The address, a copy of which has been courteously sent to me by its author, is entitled "The Etiology of Tubercular Disease." Koch first made himself known by the penetration, skill, and thoroughness of his researches on the contagium of splenic fever. By a process of inoculation and infection he traced this terrible parasite through all its stages of development and through its various modes of action. This masterly investigation caused the young physician to be transferred from a modest country practice, in the neighborhood of Breslau, to the post of Government Adviser in the Imperial Health Department of Berlin. From this department has lately issued a most important series of investigations on the etiology of infective disorders. Koch's last inquiry deals with a disease which, in point of mortality, stands at the head of them all. If, he says, the seriousness of a malady be measured by the number of its victims, then the most dreaded pests which have hitherto ravaged the world—plague and cholera included—must stand far behind the one now under consideration. Koch makes the startling statement that one seventh of the deaths of the human race are due to tubercular disease, while fully one third of those who die in
