80 
for showing the prevalence of disease, and upon the same 
scale. An alteration in the extent of this scale is neces- 
sary in the year 1826, as the early observations are much 
less minute than those after this date, and include a smaller 
number of spots. Both series will suffice for the purpose 
of comparison with the mortality periods. 
I must say at once, however, that I have been unable to 
discover any definite relation between them. 
In the case of scarlet fever, there are truly some very 
curious coincidences between the rise and fall of the 
disease, along with the number of new spots appearing on 
the sun, notably in 1848, 1856, 1859, 1867, and 1870 (see 
diagram), but a little further scrutiny will show that at other 
times, as in 1843, 1850, 1854, and 1860, the extreme height 
of the disease corresponds with a low sun-spot period, 
and vice versa. 
2. In speaking of possible cosmical causes, it is right 
also to mention the theory of pandemic waves, originated 
by Dr. Lawson, Deputy Inspector General of Army Hos- 
pitals. 
He believes that there exist world- wide influences afiecting 
epidemics — influences that coincide in some way with the 
isoclinal magnetic lines ; and from observations upon 
diseases in the army, he endeavours to show that there is 
a law by which “ a series of morbific causes originate, or at 
all events become apparent, in the southern hemisphere, 
and are propagated from that to the northern with great 
regularity.” “These waves occupy about two years in 
passing over a given station, the mortality from fevers and 
other epidemics increasing during their passage, and sub- 
siding again as they move onwards.” (Trans. Epidem. Soc., 
vol. ii., p. 95.) I do not now offer any opinion upon the 
value of this hypothesis, but I may point out that it can 
have very little bearing upon the question now before us. 
It regards rather the rate of progress and the geographical 
