294 Epidemics. 



netic theory or observations ; since the historical data had 

 heen arrived at some years before the magnetic observations 

 had been brought under notice. 



The two works, from which the short abstract upon 

 terrestrial magnetism is given, are, first, Sir W. Snow Harris's, 

 F.R.S., "Rudimentary Magnetism, "in Weale's Series, 1850; 

 and, second, the article " Magnetism," in the second volume of 

 " Natural Philosophy," published by the Society for the Pro- 

 motion of Useful Knowledge. Much progress has been made, 

 or theory suggested, since these works, but nothing that has 

 materially shaken the outline broadly and yet briefly given 

 in them. 



It will be said that, between the time for the completion 

 of an oscillation wave and its return, and a certain 

 assumed historical data of 640 to 650 years, there is a lucky 

 coincidence, and nothing more ; but, as it is quite an unde- 

 signed coincidence, the historical data being assumed years 

 before the oscillation wave was known, perhaps such a 

 coincidence is worth while being considered. 



As we have now arrived at a point where some general 

 theory must be assumed as having some co-relation to vital 

 physics and epidemics generally, a short summary of ob- 

 jections, and of things approved of in relation to some final 

 theory or explanation, will be necessary. 



ist : If the light and heat of the sun, aided by the reflected 

 light of the moon, is equal year by year, and, with the ex- 

 ceptions of eclipses, spots on the sun, and comets, may be 

 counted as actually invariable, it is legitimate to infer that 

 they are not the cause or causes of the great variations of 

 temperature, drought, excessive rain-falls, snow-storms, and 

 frost, which occur year by year, or every few years, in all 

 parts of the globe, and of such magnitude and variety as 

 to be the source of great care and anxiety in our clothing, 

 gardening, farming, and grazing operations ; that suffering 



