62 Sanitary Science in the United States : [January, 
have served as models for the conduct of similar investiga- 
tions in various other portions of the United States. Prof. 
Cook has been engaged for several successive summers in 
running a series of levels over much of the densely-popu- 
lated water-sheds of the Hackensack and Passaic, with 
similar objects; and recently a most minute inquiry has 
been made into the soil, contour, and drainage of Hudson 
County, by Mr. L. B. Ward, C.E. He has determined how 
much of its area — which includes the communities of Jersey 
City and Hoboken, and the smaller towns of Harrison, 
Kearney, North Bergen, Union, Weehawken, and Bayonne 
— is upland, how much is marsh, what portion is rocky, what 
occupied by soil of various kinds, and, where possible, the 
nature of the sub-strata, with the population on each traCt, 
and their condition in regard to sewerage and drainage. 
The ability of each variety of underlying rock, serpentine, 
sandstone, and trap, to carry off surface water, is considered, 
with the corresponding influence upon the surface tempera- 
ture, dryness, and salubrity. When we consider the abrupt 
changes of habitat over this crowded area, it will be seen 
that it offers a field peculiarly favourable for the study of 
the effeCt of surface condition upon the rates and causes of 
mortality. Most fortunately the vital statistics of this dis- 
trict have been tabulated with exceptional fulness and accu- 
racy, under the superintendence of the President of the 
Health Board, Dr. L. H. Elder. These statistics have been 
investigated by Mr. E. H. Harrison, C.E., of Jersey City, 
with extreme care. He has plotted upon a working map 
every case of fatal illness arising from insalubrious environ- 
ments, each disease being indicated by a distinctive character. 
Other maps are in course of preparation, showing the rela- 
tions of surface, contour and drainage of soil, of rock, of 
sewerage, and relative density of population over the same 
area. 
IX. Upon the Composition of the Atmosphere . 
In conclusion, I hope I may be permitted to say a few 
words with regard to one topic of sanitary science which 
for a long time has more particularly interested me, and 
which at present is the subject of especial study — the com- 
position and purity of the atmosphere. As communities 
grow more dense, and factories multiply, the sources of 
aerial impurity augment in a rapidly growing ratio. In 
England the Government has been forced to appoint an 
inspector, the celebrated Dr. Angus Smith, who has made 
