F38 



INTRODUCTORY 



THE material in this book can be absolutely relied upon. In using it, the 

 student may be sure that he is dealing with master minds, each of whom has 

 made a specialty of the science of which he treats. The editor has kept 

 steadily in view the duty of a compiler. He has refrained from making 

 digests, compends, or summaries of the works reviewed. He has not under- 

 taken to advance any opinion, theory, or creed, but simply to give the fairest 

 possible picture of the present state of science consistent with the primary 

 purpose of the work as a volume of illustrations. Where eminent men differ 

 in opinion, conflicting views have been allowed expression, leaving the name 

 and authority of each author to answer for his own statements. The record- 

 ing of a scientific opinion is not its advocacy, and that even leaders in science 

 may well change their views with advancing knowledge is abundantly shown 

 in the selections given, and freely admitted by the foremost among them. 



In obedience to the primary and controlling purpose of scientific illustra- 

 tion, whatever in science can throw a "side-light" upon some intellectual, 

 moral, political, industrial, social, or religious truth has been seized wherever 

 found. The titles and location of topics are thus not what would be found in 

 a scientific hand-book, which would place all matter treating of glaciers 

 under glacier, of oxygen under oxygen, of volcanoes under volcano, etc. It 

 is not primarily for the astronomical, geological, chemical, or other scientific 

 teachings that the selections have been made, but for some truth relating to 

 humanity, which they illustrate. 



At the same time, it is believed that the selections will be found of 

 exceeding interest for their own sake, and that they will open to many readers 

 vistas of the wide reach of science, such as their special studies have not pre- 

 viously brought to their view. The minister, the teacher, or the busy worker 

 in any profession, even if he devotes his spare time to science, can scarcely 

 hope for extensive knowledge in more than some one of its many departments. 

 Through these pages flashes of light will come to him from all, and he will 

 thus gain a fuller view of the grand unity toward which all are tending. 



Of the use of scientific illustrations in speaking or writing, it may be 

 said that they are in harmony with the spirit of the age, which is preemi- 

 nently scientific ; that they have not the hackneyed character of the numerous 

 popular anecdotes or of the stock illustrations long current in classic litera- 

 ture, and that they especially impress the thoughtful mind, as dealing with 

 facts. However theories may change, the movements of suns and planets, 

 the combinations of chemistry, the fossils and strata of geology, the proper- 

 ties of heat, light, and sound, the marvels of electricity, and the infinitesimal 

 world of the microscope are facts, ascertained and demonstrable. The mind 

 is there upon sure ground, and the use of such facts in illustration gives a 

 sense of certainty and reality to the thoughts they are employed to illustrate. 



The selections here given are not from works on so-called ' ' popular sci- 

 ence," where the element of popularity often quite swamps the scientific, 

 where uncertified facts are given on the testimony of anonymous witnesses, and 

 where the suspicion is often inevitable that the occurrence happened for the 

 sake of the illustration. This work is based upon the belief that the essentials 

 of science are simple enough for the untrained mind, and that whatever of 

 abstruseness it contains is in processes or in their necessary technical terms, 

 and that there are none who can state the essentials more clearly than those 

 who know them most thoroughly at first hand the leading specialists in the 



