Spectral evidence

“ But it must be remembered that when physiologists pretend to settle the whole question of apparitions by the theory of spectral illusions, they are exactly in the same predicament. They can supply examples of similar phenomena; but how a person, perfectly in his senses, should receive the spectral visits of, not only friends, but strangers, when he is thinking of no such matter—or by what process, mental or optical, the figures are conjured up—remains as much a mystery as before a line was written on the subject. ”

“ Structure revealed by microscopic examination must be compared with that of known substances; chemical and spectrographic analysis has to be checked by reference to a codified series of earlier tests; crackle on a surface can only be labelled as false if the nature of genuine crackle is known; 23 and the reading of whatever is discovered by X-ray, ultra-violet, or infra-red rays calls for comparison with verified results of previous examinations. The facts yielded by one method of investigation may by themselves not be sufficient evidence of forgery ”

“ In spectral analysis, these finders have a peculiar importance; for by means of them the precise point of the object under examination is known, to which the slit of the spectroscope in the principal telescope is directed. It is therefore necessary that the cross-wires, or in general the sights placed in the field of the finder, should correspond with great exactness with the slit of the spectral apparatus, and I had, of course, taken great care to secure this essential point. Special micrometers were also provided, to measure rapidly the height and angle of position of the protuberances. ”

“ It remains to be considered how science may hope to obtain more trustworthy evidence than we yet have respecting the corona and its changes of form, extent, lustre, and physical constitution. In the case of the prominences, we have the means of making systematic observations on every fine, clear day. It has been, indeed, through observations thus effected by the spectroscopic method that an association has been recognised between the number, size, and brilliancy of the prominences on the one hand, and the number, size, and activity of the sun-spots on the other. ”

“ The nascent science of spectrum analysis was materially promoted by Herschel. He noticed in 1819 the distinctive light-absorbing qualities of coloured media, studied the spectra of various flames, adverted to the definiteness and individuality of the bright lines composing them, and recommended their employment for purposes of chemical identification. ”

“ And if such spectral illusions can occur to people in a good normal state of health, does it not become very desirable to give us some clearer theory of them than we have at present?
But there is a third presumption to which the skeptical may have recourse, in order to get rid of this well-established, and therefore very troublesome fact, namely, that Miss Lee was ill, although unconscious of it herself, and indicating no symptoms that could guide her physician to an enlightened diagnosis; and that the proof of this is to be found in the occurrence of the spectral illusion ”

“ These variations in spectra depend upon the fact that any substance that is heated sufficiently to emit light whether in the heavens or on the earth, will give a spectrum. If it be a solid or liquid body, we shall have what is called a continuous spectrum—that is, a colored band bright from end to end, with no sign of any dark or bright lines about it. ”

“ Every substance, you know, is, when radiating light, characterized by what at first appears to be almost a haphazard set of spectral lines without relation to one another. But they are related by mathematical laws and the apparent haphazard character is only the result of our lack of knowledge of how to interpret the results. ”

“ The experimental case of spectral analysis is incomparably simpler and less open to dispute. It is without doubt a discovery of fundamental importance bearing all the characteristics of originality, for no predecessors are discernible. I have always felt a little dissatisfied with the fact that it required two men to think it out, that a duo of minds was necessary for one act of thought which appears quite uniform, elementary and inseparable from the intuition of a single mind. ”

“ A SCIENCE, like a child, grows quickest in the first few years of its existence; and it is therefore not astonishing that, though twenty years only have elapsed since Spectrum Analysis first entered the world, we are able to speak to-day of a modern spectroscopy, with higher and more ambitious aims, striving to obtain results which shall surpass in importance any of those achieved by the old spectroscopy, to the astonishment of the scientific world. ”

“ Let us use the term spectral index (s) to define a number expressing the spectral character of a star. Then we may conveniently define this conception in the following way. Let A0 correspond to the spectral index s = 0.0, F0 to s = +1.0, G0 to s = +2.0, K0 to s = +3.0 M0 to s = +4.0 and B0 to s = -1.0. Further, let A1, A2, A3, &c., have [Pg 18] the spectral indices +0.1, +0.2, +0.3, &c., and in like manner with the other intermediate sub-classes. Then it is evident that to all spectral classes between B0 and M there corresponds a certain spectral index s. ”

“ If the body is moving away from the spectroscope the shifting of the spectral lines will be in the opposite direction, towards the red end of the spectrum. In this way we have discovered and measured movements that otherwise would probably not have revealed themselves unmistakably to us for thousands of years. In the same way we have watched, and measured the speed of, tremendous movements on the sun, and so gained proof that the vast disturbances we should expect there actually do occur. ”

“ Stars with fluted spectra indicate the presence of vapours of the metalloids or of compound substances, while the reversed flutings indicate the presence of carbon. These conclusions have been reached by careful laboratory experiments which are now carried on at the same time as the spectral examination of the stars and other heavenly bodies, so that each peculiarity of their spectra, however puzzling and apparently unmeaning, has been usually explained, by being shown to indicate certain conditions of chemical constitution or of temperature. ”

“ Yet Wollaston years after passed his beam of light through a slit instead of a round hole, and the lines of the solar spectrum were for the first time visible. It was still left to Fraüenhoffer and others to interpret their meaning, and to-day men of science are able to speak of the elements which enter into the composition of distant worlds, and you or I by the aid of the spectroscope could detect infallibly the presence of blood in solution, in amount so small that our microscopes would be useless in the search. To take an illustration which more nearly concerns us to day. ”

“ For in point of fact, the very principle on which our recognition of the bright lines depends involves the inference that matter whose light would not be resolved into bright lines would not be recognizable at all. The bright lines are seen, because by means of a spectroscope we can throw them far apart, without reducing their lustre, while the background of rainbow-tinted spectrum has its various portions similarly thrown further apart and correspondingly weakened. ”

“ The spectral person may be the self, or it may be another or a congress of others. When the voices of others are falsely perceived as persons, these others are specters.
Specters may be classified by senses deceived, and subclassified by the agencies through which they are produced. The class of specters derived from hallucinations of vision we will treat as thus subclassified, for the purpose of illustrating the doctrine. ”

“ But are we not trusting our spectroscope too much? Surely, having found it to be trustworthy for terrestrial substances, where its statements can be verified by man, we are justified in accepting its testimony in other like cases; but not when it gives us information about things in the sun, where its testimony cannot be directly verified by man? ”

“ But persons of real inquiry will see that first, experience does not bear out the asserted frequency of the spectre, without the alleged coincidence of death: and secondly, that if the crowd of purely casual spectres were so great that it is no wonder that, now and then the person should have died at or near the moment, we ought to expect a much larger proportion of cases in which the spectre should come at the moment of the death of one or another of all the cluster who are closely connected with the original of the spectre. ”

“ We have said that every substance has its own distinctive spectrum, and it might be thought that, when a list of the spectra of different substances has been prepared, spectrum analysis would become perfectly straightforward. In practice, however, things are not quite so simple. The spectrum emitted by a substance is influenced by a variety of conditions. The pressure, the temperature, the state of motion of the object we are observing, all make a difference, and one of the most laborious tasks of the modern spectroscopist is to disentangle these effects from one another. ”

“ The spectroscopic analysis, when applied to the same problem, walks upon slippery ground and must take heed lest it also fall. The alleged displacement is a nice quantity, and instrumental sources of error have been pointed out which may explain away the whole of it. I lay no stress upon the large difference between Vogel and Huggins in the quantity of motion which spectrum analysis ascribes to Sirius, inasmuch as the direction of the motion is the same. We do not yet know all the elements which the earth contains. The spectroscope has already added four to the number. ”

“ If I have a transparent body and allow light sent out by a body giving a continuous spectrum to fall through it, I often observe that the transparent body sifts out of the light falling through it certain kind of rays. Spectra are thus produced which are called absorption spectra, because the body which is under examination does not send out any light, but absorbs some vibrations which are made to pass through it. It is an important fact that a molecule absorbs just the rays which it is capable itself of sending out. ”

“ Again, if we have an extremely complex light-source, let us say a solid and a mixture of gases giving us light, and we allow the light to enter, so to speak, indiscriminately into the spectroscope, then in each part of the spectrum we shall get a summation—a complex record—of the light of the same wave-length proceeding from all the different light-waves. But if by means of a lens we form an image of the light source, so that each particular part shall be impressed in its proper place on the slit-plate, then in the spectrum the different kinds of light will be sorted out. ”

“ These observations and experiments doubled the field of investigation opened to spectrum analysis. Not only could the incandescent atmospheres of the sun and the stars now be made to reveal their nature and their composition to us, but our researches might also be extended to objects having a still greater interest for us. We could at once take our own atmosphere for an object, investigating high and inaccessible regions, and making analyses in them which could not be attempted by any other means. ”

“ The spectroscope, however simple or complex it may be, is an instrument which allows us to observe the image of the slit through which the light enters it, in the most perfect manner. If the light contains rays of every wave-length, then the images formed by each will be so close together that the spectrum will be continuous, that is, without break. If the light contains only certain wave-lengths, then we shall get certain, and not all, of the possible images of the slit, and the spectrum will be discontinuous. ”

“ Indeed, had nineteenth-century science accomplished nothing else than the discovery of spectrum analysis, it would have marked the beginning of a new epoch. By this device man is put in communication with every considerable body in the universe, including even the invisible. ”

“ The great difficulty of interpreting the results of the spectroscopic analysis of the sun arises from the circumstance that we have no means of learning whence that part of the light comes which gives the continuous spectrum. When we recognize certain dark lines, we know certainly that the corresponding element exists in the gaseous form at a lower temperature than the substance which gives the continuous spectrum. ”

“ The question is not, How have we conducted, unless our conduct be such as invalidates our evidence: for we are liable to evil every day; but, How has the Spectre conducted? and who could she be? It has been frequently reported among people at a distance from this scene, for more than twenty years, that the whole business was an artifice, and fairly proved to be such. We who believe the existence of the Spectre, have thought that this inaccurate on dit has had currency long enough. ”

“ But as a science progresses it is often possible to direct the way “by showing the kind of data which it is especially important to improve,” and particularly is this the case for astrophysics. In the improvement of the old data, by far the most important requirement is some method of standardizing the intensities of spectrum lines, and of measuring their width, energy distribution, and central intensity. This involves a very difficult and necessary piece of photographic photometry. The problem is an old one that has defied attack for a long time past. ”