70 THE POPULAR SCIENCE MONTHLY. 



well as if the ideas had taken form in words. In order to be success- 

 ful, this would require a very intimate acquaintance with the friend's 

 habits of thought. In fact, we all try to interpret the thoughts of 

 others during silence, but we are generally wide of the mark, because 

 we do not know the peculiar law of association of ideas applicable to 

 each person. There is a general process by which one idea suggests 

 another in all minds, but there are also j^articular variations. Never- 

 theless, unless the person is on his guard, fully seventy-five per cent, 

 of his ideas will be known to any one who is accustomed to following 

 the thoughts of others. The first thoughts, which arise in the mind 

 automatically, are limited in number, because the connection with 

 more remote ideas has not yet been made. It is probable that with 

 increased knowledge of the j^eculiar laws of mental action, great skill 

 will be shown in thus following the ideas of others, and it is clear that 

 such a science of mind-reading would be built upon metaphysical data, 

 just as mathematical data are now necessary factors in estimating the 

 distance and motion of a planet. In some respects the limit of mental 

 penetration may not be as absolute as we imagine. It is certainly not 

 advisable to set limits like those astronomers who claimed that they had 

 discovered the center around which the visible universe is revolving 

 in a mighty orbit. It was found that this so-called center was describ- 

 ing a vast arc of a circle around another center inconceivably distant. 

 The discoveries of the past indicate that others as important are to be 

 made. The horizon recedes, revealing new objects. 



In the light of past discoveries it seems highly improbable that so 

 important a physiological gift as a sixth sense could come to us sud- 

 denly and mysteriously. This is not the manner in which Nature 

 works. Everything is paid for, and our advantages come only from 

 work and its accompanying natural growth, or by the hereditary trans- 

 mission of a fortunate balance of powers in a line of ancestors. The 

 first impulse arises from the necessity of work, and from the actions of 

 events which stimulate the ingenuity. The increased activity is ac- 

 companied by an increase of fiber or power of continuance. Tyndall 

 has admirably illustrated the fact that this law of mental supply and 

 demand applies with precision to the processes of nature : " No parti- 

 cle of vapor was formed and lifted without being paid for in solar 

 heat. There is nothing gratuitous in physical nature, no gain with- 

 out equivalent expenditure." It is our tendency to look for theatrical 

 or imposing manifestations of human power not paid for by work, and 

 when a result appears mysterious owing to our ignorance of its source, 

 we too often settle the difficulty in accordance with a convenient and 

 visionary theory. In this way we hear a coincidence called a prophetic 

 dream. No one has adequately estimated the enormous number of 

 dreams that drift through the mind during a lifetime, and when a 

 dream coincides in a measure with an event which takes place long 

 afterward, the assumption then is that some dreams are of a pro- 



