May 23, 1872] 



NATURE 



65 



way secured, very slight and delicate in its nature, it is 

 true, but yet one upon which implicit reliance can be 

 placed when undertaking astronomical measurements. 

 To those more particularly interested in operations of 

 this kind, we may mention that a total exposure of six 

 minutes sufficed for the depiction of these heavenly bodies 

 in the camera. 



Turning to another branch of the subject — micro- 

 photography — we find the camera used for several purposes 

 as important almost as those to which we have just referred. 

 In the study of medicine, for instance, and the many sec- 

 tions of Natural History, photography lends a helping 

 hand, so firm and true that we are at once guided to our 

 destination. The large, clearly-defined diagrams of micro- 

 scopic objects and medical preparations, which we are wont 

 to see at many schools and colleges, cannot be prized too 

 highly, forming as they do the best and most reliable proofs 

 in support of facts and data, and being indeed of value 

 alike to the professor as the student. And perhaps while 

 treating on this particular subjeat, we may be allowed to 

 refer also to the use made of the micro-camera during the 

 siege of Paris for conveying news from and to that city. 

 We have all (heard how batches of private letters and 

 whole sheets of newspapers have been reduced by means 

 of photography to within the most insignificant limits, 

 and produced upon a transparent pellicle, of which a 

 pigeon might without inconvenience carry several under 

 its tail, and how these precious films, on arrival at their 

 destination, were forthwith placed in an enlarging ap- 

 paratus or under a microscope, to be amplified to their 

 original dimensions. Paris, it is said, contained upwards 

 of a thousand pigeons qualified to act as messengers, and 

 when it is asserted that on one occasion one of these 

 birds arrived at Tours with several thousands of private 

 messages and despatches, we ought by no means to be 

 surprised that the communications between the French 

 metropolis and the provinces were so numerous and 

 frequent. 



In the chemical, physical, and meteorological sciences, 

 and even in that of war, photography aids in many ways, 

 and thus helps to the advancement and progress of our 

 knowledge of these matters. But the art, or art-science, 

 as we may call it, has in several instances done some- 

 thing more than render yeoman's service to higher at- 

 tainments ; it has also been the means of discovering 

 phenomena which could by no other means have been 

 ascertained. In illustration of this may be mentioned the 

 recent researches of Dr. Ozanam, undertaken for the pur- 

 pose of defining the character of the pulsations of the 

 heart ; an investigation which has l:)rought to light facts 

 of considerable physiological importance. The instru- 

 ment used by Dr. Ozanani was a thin India-rubber 

 reservoir of mercury, having a glass tube attached, in 

 which the quicksilver mounted to a certain height ; the 

 reservoir, on being placed in the vicinity of the patient's 

 heart, was influenced by the beating of the latter, and the 

 rise and fall of the mercury in the tube was thus made to 

 indicate the ebb and flow of the blood, precisely in the 

 same manner as a barometer registers the variations of 

 the atmosphere. Behind the tube was arranged, by means of 

 clockwork, a moveable strip of sensitive paper, or other 

 suitable material, and this, as it ran along, was impressed 

 by light, and received, in the form of an undulating line, 

 a register of the fluctuations of the mercury column. The 

 sensitive film passed along at the uniform rate of a centi- 

 metre per second, so that, presuming there to be one 

 pulsation in that period of time, the wavy line representing 

 a single beat would occupy the space of one centimetre. 

 Of course, by enlargingtheresulttotenor twenty diameters, 

 it was then, as may be supposed, easy to see what had 

 taken place during the hundredth or thousandth part of 

 a second, or beat, and the knowledge thus acquired. Dr. 

 Ozanam believes, will be highly useful in preparing the 

 diagnosis of a patient, One fact, of itself very important, has 



already been discovered by the aid of this ingenious instru- 

 ment, viz., that not only as Dr. Maurey had before asserted, 

 there exists dicrotism, or a double beat, in the normal pulse, 

 but that the pulsation is even triple and quadruple in 

 its action. The photographic line showed indeed that the 

 column of mercury (representing of course, the blood in 

 the arteries) bounded with one leap to the top of the scale 

 and then descended again to its original level by three or 

 four successive falls. Four descriptions of dicrotism have 

 in this way been proved to exist, the fall of the pulse 

 sometimes taking place in successive horizontal lines and 

 sometimes in ascendant lines, the column reascending 

 two or three times before falling altogether. 



Another instance of scientific discovery by aid of photo- 

 graphy is afforded in the observations of the spectrum by 

 means of the camera. In Rutherford's picture of the solar 

 spectrum obtained in this manner, there are many por- 

 tions and lines shown (the ultra-violet for instance) which, 

 while imperceptible to the retina of the eye, impress 

 themselves very distinctly upon the sensitive film ; and 

 thus the presence of phenomena is proved of which but 

 little was previously known. Of course the eye again 

 descries certain lines, the yellow ones, which are without 

 action upon the negative plate, and are not, therefore, 

 recorded in the photograph, and thus it is only by care- 

 fully noting the results of both methods of observation 

 that a true reproduction of the spectrum is obtainable. 

 As a fact, we may mention, that single lines which are 

 but faintly rendered in the Angstrom and Kirchhoff tables 

 have been recorded by photography as well-marked double 

 lines, while in some instances actually Rutherford shows 

 indications by means of the camera of which there 

 appears no vestige whatever in the records of other 

 scientific men. In certain spectroscopic observations 

 therefore, where special reliance is required to be placed 

 upon the results, not only must an ocular observation be 

 made, but the photographer's evidence must also be taken 

 before any conclusions can be drawn from the aspect of 

 the spectrum. 



And before concluding we must not forget to refer to a 

 still more recent instance in which photography has be- 

 friended the scientific investigator ; we allude to the suc- 

 cessful, although perhaps somewhat imperfect attempt which 

 has been made by Prof. Young, to photograph the pro- 

 tuberances of the sun in ordinary d lylight. A distinct 

 reproduction of some of the douljle-headed prominences 

 on the sun's limb has thus been obtained by the Pro- 

 fessor ; and although as a picture or mathematical re- 

 cord the impression may be of little value, still there is 

 every reason to believe, now that the possibility of the 

 operation is known, that with better and more suitable 

 apparatus an exceedingly valuable and reliable record 

 may be secured. Prof. Young employed for the purpose 

 a spectroscope containing seven prisms, fitted to a 

 telescope of 6J- inch apperture after the eyepiece of 

 the same had been removed ; the miniature camera, 

 with the sensitive plate, was attached to the end of the 

 spectroscope, the eyepiece of which acted in the capacity 

 of a photographic lens, and projected the image on the 

 collodion film. The exposure was necessarily a long one, 

 amounting to three minutes and a half, and for this 

 reason, as likewise on account of the unsteadiness of the 

 air and the mal-adjustment of the polar axis of the equa- 

 torial, causing the image to shift its place slightly, the 

 details of the image wore somewhat blurred and destroyed. 

 Moreover the eyepiece of the spectroscope was unsuitable 

 for photographic purposes, and only in the centre yielded 

 a true reproduction of the lines free from any distortion. 

 A lai-ger telescope will be required to secure a more de- 

 fined image, and then, if more strict attention is paid to 

 the clock-work arrangements and to the chemical mani- 

 pulations, we may anticipate that a really valuable and 

 important result will be obtained by this novel mode of 

 observation. H. Baden Pritchard 



