Improving Natural Knowledge 35 



morals, which keeps the plague from our city; but, again, 

 that it is the improvement of our natural knowledge. 



We have learned that pestilences will only take up their 

 abode among those who have prepared unswept and un- 

 garnished residences for them. Their cities must have 5 

 narrow, unwatered streets, foul with accumulated garbage. 

 Their houses must be ill-drained, ill-lighted, ill-ventilated. 

 Their subjects must be ill-washed, ill-fed, ill-clothed. The, 

 London of 1665 was such a city. The cities of the East, 

 where plague has an enduring dwelling, are such cities. 10 

 We, in later times, have learned somewhat of Nature, 

 and partly obey her. Because of this partial improve- 

 ment of our natural knowledge and of that fractional 

 obedience, we have no plague; because that knowledge is 

 still very imperfect and that obedience yet incomplete, 15 

 typhus is our companion and cholera our visitor. But it is 

 not presumptuous to express the belief that, when our 

 knowledge is more complete and our obedience the ex- 

 pression of our knowledge, London will count her centuries 

 of freedom from typhus and cholera, as she now gratefully 20 

 reckons her two hundred years of ignorance of that plague 

 which swooped upon her thrice in the first half of the 

 seventeenth century. 



Surely, there is nothing in these explanations which is 

 not fully borne out by the facts? Surely, the principles 25 

 involved in them are now admitted among the fixed be- 

 liefs of all thinking men? Surely, it is true that our 

 countrymen are less subject to fire, famine, pestilence, and 

 all the evils which result from a want of command over 

 and due anticipation of the course of Nature, than were 30 

 the countrymen of Milton; and health, wealth, and well- 

 being are more abundant with us than with them? But 

 no less certainly is the difference due to the improve- 

 ment of our knowledge of Nature, and the extent to which 



