666 THE POPULAR SCIENCE MONTHLY. 



other : the one being delighted in finding out and making his way into 

 the unknown, while the pleasure of the other consists in seizing results, 

 and putting them into shape, so that they may be servants to our will. 

 The history of electricity strikingly displays these distinct aptitudes 

 and pursuits. Volta, Franklin, Arago, and Faraday, were leading dis- 

 coverers of the properties and laws of electricity. They cared far less 

 about the every-day use which might be made of the newly-discov- 

 ered force, than of gaining a complete insight into its nature, and of 

 making it the means of unlocking other secrets of the natural world. 

 On the other hand, Morse and Wheatstone thought only of electricity 

 as a means to an end, or of reaching, through some ingenious contriv- 

 ance, the means of rendering human communication, at distant points, 

 practically instantaneous. 



A knowledge of the leading facts upon which sanitary science is 

 founded is, at least, as old as history itself. It antedates the time of 

 Moses ; many of the rules of hygiene having been taught by the Egyp- 

 tian priests. But more especially within the past two centuries has 

 the knowledge of the ways in which disease is produced, and may be 

 avoided, been corrected and extended. It is within this period that 

 the first attempt was made in Europe to establish quarantines. The 

 sum of the precautions taken in London during the middle ages to 

 guard against the ravages of the plague, was the isolation of infected 

 houses, and putting a red cross on house-doors, on which were in- 

 scribed the words, " Lord, have mercy on us." 



The physician of to-day, who has devoted half as much thought to 

 the prevention of disease as to its cure, firmly believes in human abil- 

 ity to avoid nearly all the ills to which flesh is now subject. Given a 

 good constitution, and the conditions of health or sickness are almost 

 wholly in our own power. He believes this, and on precisely the same 

 grounds that the geologist believes that fossils are not what was once 

 universally believed, the primary result of the action of a plastic or 

 creative force in Nature. A like belief exists in the popular mind in 

 reference to health and longevity, though in a less positive form. 

 Families known to be of good constitution, and of ancestry noted for 

 their length of days, are not expected to be sickly and short-lived. 

 "When any member of such a family does become a permanent invalid, 

 and likely soon to die, it is a familiar expression, and notoriously true, 

 that he or she has abused the endowment inherited. 



Passing over the evidence which has convinced those the most com- 

 petent to judge in reference to the prevalence of disease the physi- 

 cians to their conclusion, that if all possessed good constitutions, and 

 lived as they ought to live, in accordance with hygienic law, there 

 would be no disease, or next to none, and death would not come upon 

 the human family through a morbid process, but by the only truly nat- 

 ural mode of dying old age ; the question arises, How do men come 

 by good constitutions? Through a course of life by progenitors for 



