1. Table showing the daily yield of Water from a Roof with varying Rainfalls.1

For any other size of roof or amount of rainfall, the numbers will be proportional.

2. Tables showing the Distribution of Positive and Negative Errors, according to Number of Events.

From a paper by H. Sowerby-Wallis, F.M.S., on Rainfall Collection, Transactions of the Sanitary Institute of Great Britain, vol. i., 1880 (Croydon Congress), p. 213.

In each case the number of chances correspond to the coefficients of a binomial whose exponent is the number of events. Thus, with 1 event we have (a+b)1 = a+b; with 2 events we have (a+b)2 = a2 +2ab + b2, and

so on.

AMERICAN APPENDIX

ΤΟ

PARKES' HYGIENE.

INTRODUCTION.

THE fundamental principles of hygiene underlying all measures aimed at the improvement of the health of mankind so carefully brought out in the preceding pages are, of course, applicable to all countries, climates, and habits of living; but there is very much that is of a practical nature, applicable to England and English ways which it would be impossible to follow in the United States, where existing conditions of climate, government, density, and movement of population are so totally different. For this reason it has been thought best to supplement the theoretical part of the treatise bearing Dr. Parkes' name by a short sketch of American practice in matters relating to public health, and the progress that has been made in sanitary science during the last few years.

Although for many years a department for the study of subjects relating to State medicine, and for the employment of such methods as would tend to improve the health of the nation, has had its place in the internal policy of England, it was not till the year 1869 that any measures looking to the same results were inaugurated in America. In that year Massachusetts created a State board of health, and gradually other States have followed her example till twenty-nine now have their departments of health.

The creation of these boards of health has been the outcome of a gradually growing public recognition of the need for concerted action in the prevention of disease, a feeling that received great impetus during the epidemic of 1878. Much of this interest is, however, due to the fact that it can now be proved that a large proportion of the deaths that occur annually from contagious or infectious diseases might be prevented, and the average duration of human life considerably lengthened thereby.

As the education of the public increased, so did the demand for accurate knowledge concerning the causes of disease and the methods for its prevention. Laws were enacted in several States creating boards of health, which should make these investigations, and the system was completed when, in 1879, Congress created the National Board of Health, whose duty it should be to make investigations into the causes and means of prevention of contagious and infectious diseases, to initiate measures of national importance, and to be a centre of information for all matters relating to public health. So valuable has been the work of this Board, during its short career of four years, that something more than a passing notice seems to be merited. The following sketch of its history and work has been compiled from notes furnished the writer by Dr. Stephen Smith, a member of the Board, to whom he feels himself greatly indebted :

"The National Board of Health was the direct outcome of the great yellow fever epidemic of 1878," which, among other valuable lessons, taught