176 THE POPULAR SCIENCE MONTHLY. 



success of jugglery and all the forms of tricks of sleight-of-hand ; au- 

 diences fancy themselves to be seeing what they do not see. Casting 

 our eyes upward to the sun and moon and stars, these heavenly objects 

 seem to move with measurable slowness across the concave surface of 

 the blue arch of sky ; and only through the deductive reasonings and 

 calculations of a Copernicus, a Galileo, a Newton, are we brought to 

 the conviction that the earth is the moving object, that the blue vault 

 but marks in the air the limitations of our vision, and that the shining 

 stars that appear as candles in the sky are gigantic worlds moving with 

 enormous velocity millions of miles away. Sitting in a railway-train 

 at a station, as the train next to us on one side begins to move, we 

 seem ourselves to be in motion, and only by looking on the opposite 

 side and steadily observing some point or object that by previous ob- 

 servation we know to be fixed, can we correct our delusion ; but in 

 practical life we are not always able to find a fixed point or object ex- 

 ternal to ourselves by which we can distinguish the subjective and 

 objective in our retinal impressions. Thus, in all human experience, 

 " truth and lies are faced alike ; their port, taste, and proceedings, are 

 the same ; we look upon them with the same eyes." ! 



Limitations of the Human Bbain in Disease. But the most 

 serious blunders of the sense of sight, or indeed of the other senses, 

 and indeed of reasoning in general, come from confounding the subjec- 

 tive with the objective. In certain states of the system, which are not 

 rare but very common, and which may be either temporary or perma- 

 nent, the brain has the power not only of modifying the impressions 

 made by external objects over the retina, but of originating impressions 

 even when there are no external objects corresponding to those impres- 

 sions, and the individuals may have no way of distinguishing subjective 

 from objective visions, or find it very difficult to do so without outside aid. 



1 A critic of Prof. Tyndall, indignant that the philosopher would not accept the reign- 

 ing delusions of the day, declared that, when called upon to investigate any object, he 

 would look at it, listen to it, touch it, taste it, and smell it, and then not believe it. The 

 critic was not aware that, instead of censuring Prof. Tyndall, he was really giving one of 

 the highest compliments that can be given to a scientific man. 



This over-estimate of the capacity of the human brain and senses, united with the 

 present chaotic state of the principles of evidence, aifects injuriously not philosophy alone 

 but practical life as well. In medicine, for example, it has for ages been the fashion to 

 ignore or deride symptoms of a purely subjective nature, that have no corresponding 

 lesions or morbid appearances that the aided or unaided senses can discover, and for the 

 study of which it is necessary to depend on deductive reasoning and the statements of 

 patients. This is in general the explanation of the fact that many of the most frequent 

 and distressing diseases, such as nervous exhaustion, hypochondriasis, hysteria, hay-fever, 

 and allied nervous affections, although of the highest scientific and practical interest, have, 

 nntil quite recently, been almost entirely neglected, and the agonizing symptoms connected 

 with them arc dismissed as trifling if not imaginary. A broken leg every one can see, and 

 touch, and handle ; but an exhausted brain, oftentimes a far more serious matter, is passed 

 by, and even its existence is doubted merely for this, that it is out of reach of the eye 

 and the microscope. 



