“Even the colloid practically battles the microscope. In the ordinary atmosphere, merely cloudy impressions can be obtained. How then is the presence of any of these tiny particles discovered? It is very simple, when the method is disclosed. The colloid cannot be seen, but it makes a shadow on an electric spark as it passes by. So when the presence of a colloid is suspected, its shadow on an electric spark betrays it.”
“Pardon me, Doctor, for interrupting you,” broke in the bewildered Mr. Bailey, “but if this discussion has any bearing on the death of Jim Craighead, I would like to know, if these particles you are talking about, are so small that they cannot be seen with the strongest microscope, how it helps you any to know they make a shadow on an electric spark. In fact, how do you know they make a shadow on an electric spark?”
“You may have read at times, Mr. Bailey,” replied the doctor, “announcements that astronomers had located a star known through mathematical calculations to be at some point in the heavens, which the telescope has been unable to penetrate. Well, the speed of light, which is 186,000 miles a second, helps us. A photograph of the heavens will sometimes reveal something which the eye could not see. So, a photographic plate will sometimes catch the smaller particles as well as the largest stars, too far away to be seen.
“If you consider the light as moving in waves it is easier to understand what effect light waves have on these discoveries. Artificial light travels in waves farther apart than in the case of natural light. The waves of this kind of light are so far apart that the colloid or small microbe can lie between the waves and make no impression on the eye or on the photographic plate.” The doctor here took a sheet of paper and hastily made a sketch which he showed to the jurors and the coroner.
Artificial light waves:
“The waves of natural light are closer together, but still too far apart to catch much of the smallest germs, like that of cancer, or the colloid, to advantage.” The doctor made another sketch.
Natural light waves:
