Show POTOGRA lNG TilE NVSBLL IAn I I-An Englishf Scientist Takes Pictures of That Which tieS I f tie-S Eye Cannot See I Special Correspondence London Dec 2The instantaneous electric spark has been used by many scientists toillustrate certain physical I1 i i Phenomena Professor C V Boys used it to photograph flying bullets Profes1 sor Vorthington to photograph theE i the-E spash of a drop Lord Rayleish to phoj 1 i tOtfraph streams of bubbles etc The i I 1 latest application is the photo photography 1 j of ripples It has been accomplished I I by J H Vincent of the Royal College < of Science London 0 Most of the ripples which can be pro duced on the surface of mercury are Invisible to the naked eye because the duration of the sensation produced by 1 ft a luminous impression on the retina J 41 lasts for only oneeighth of a second Mercury ripples are nratb always too Shot to allow of the eye picking them out therefore we have to resort to the instantaneous method m order to see them Mr Vincent is the first expei nncnter who has succeeded in obtaining photographs photo-graphs of ripple on a mercury surface To some minds the great amount of care and preparation needed for the photography of mercury ripples may seem out of all pnp < rtion to the result obtained It is < jun > true that they will not create a new industry nor revolutionize revolu-tionize an old one Indeed it Is impossible 0 impossi-ble to see how they can be applied to any business ends Strange as it may seem this quality endears them to the scientific man They help to illustrate i in a new way some of the well known TTIT frast If P V I iI fl If Photographs of Mercury Hippies These Ripples Have Never Been By Human Eyes laws of nature they show that patience II and determination can overcome almost al-most all difficultiesand this is quite i s enough for the latter I j t If we throw a stone into a pool of I water we produce a series of motions I on its surface which go by the name ol i aves ripples or undulations and w e t experience no difficulty in seeing these i waves with the naked eye because their length is comparatively large Scientists Scien-tists determine the length of a wave motion whether in the air the ether j the sea or in any liquid surface by t measuring the distance between crest i and crest The length of a wave is in fact the distance from crest to crest Now it is quite possible to produce little lit-tle waves or ripples tn a liquid surface which are so small which follow each other with such Great frequency and which pass so quickly before the yeas ye-as to be perfectly invisible Those who have attended scientific lectures of course know the means taken to render visible these ordinarily invisible little waves They are shown I either by what is known as the stro bo eopio method or else by the production pro-duction of an instantaneous light The I first method has often been shown at public lectures by Professor C V Boys I and is as follows OLD AXD NEW METHODS A watei surface focubsed on the I screen appears unaffected by being touched with the point of a feebly j soumiiitr tuning fork Directly however how-ever the light is intercepted with a j revolving disk rotating in time with I the fork the ripples are seen clearly j enough through the opening of the I r disk This method is akin to the instantaneous i I in-stantaneous shutter employed by the I photographer or the cinehetograph tr and has been used with great ef fet by Professor Maybridge in his photographs of trotting horses etc It I will a once be seen that it comes to the same thing whether we look at the ripples by an instantaneous light or I whether we use somE mechanical device de-vice and allow th ° ripples to be submitted I sub-mitted to brief periods of light Instantaneous I In-stantaneous photography is not quite I a defensible term because no photography j pho-tography can be really instantaneous j but the time taken is so extremely minute I mi-nute that the phrase may be allowed 1 to pass We can employ either the magnesium flashlight which vanes I from onet nth to onefifteenth of a second or we may use the electric I spark Professor Rood of New York some time back made some experiments I experi-ments on the duration of the discharge I i of a Leyden jar and also on that Oi i lightning and he proved that in certain i cases the duration of an electric spark i across the knobs of Leyden jar I charged from a Wimshurt machine was a > > short as one twentyfive millionth i mil-lionth part of a second of time i Now in order to bring home the full 5B N force of this statement let me borrow an illustration I once heard Lord Raj leigh use A million seconds is about I 12 days and nights 25000000 seconds is nearly a earso that the turn mru I I pied by the spark in Professor Hoods i experiment ic i about the same fraction I 4 f of one second that one second is of a 0 year I Mr Vincent attains his results by I the sudden illumination of an electric spark The spark is about half a centimeter cen-timeter in length and it lasts about the one two hundred thousandth part of a second Not so short a period as one twentyliv millionth part of a second which it will be remembered was the Time of the park employed by Professor Profes-sor Rood hut nevtrtheless an incredibly incred-ibly short period To determine the duration of such a spark < which maybe may-be said to have scarcely any being at all for it dies as soon as it is born is a difficult task The scientist has re courre to that wonderful weapon the revolving mirror first employed by Whcatstone and since used to determine deter-mine the velocity of light Mr Vincent uses a ioml spark produced pro-duced ii the usual way by crr > n < ctmg a Wimshursl machine with the knobs = of a Leyden jar which is generally I 15 centimeters across to increase the biightness of the first spark In the Illustration we see the Wims hurst machine and the wires leading from it to the four Leyden jars The Srnt spark gap from which the light proceeds to illuminate the mercury sur kface is = placed near the top of that gal I lowslike structure to the left of the I camera The second spark gap is on I the immediate right of the four jars i When the Wimshiirst is turned the park plays across the two spark 1 gaps and the light from the first is I nadc to fall on a lens to the left of i the Stand m pie path of the light A 1 second lens similar in all respects to I Lheuirst converges the reflected light I i fi < am the mercury surface into the pho graphic camera j Mr Vincent sets up his iipples in the trough of mercury which can be seen I below the camera by agitating the i surface of the mercury by a stylus of glass attached to one prong of a vibrating vi-brating tuning fork plainly visible in i 1 the photograph ilr Vincent either I givfs the prongs of the tuning fork a i blight blow or else he electrically es I cites a second fork connected by a thread to the exciting fork This hatter is the most satisfactory method both folks behaving in identically the same 1 manner NEW FACTS SHOWN IN PHOTOGRAPHS I PHOTO-GRAPHS The first photograph here reproduced shows us a series of circular waves setup II set-up in the trough of mercury by a sr1 i gle stylus of glass attached to a vibrat ins tuning fork When the fork was touched the stylus was depressed at the black spot in the middle of the picture and the beautiful little ripples invisible invis-ible to the naked eye but by the skill of the operator made visible in a photograph photo-graph were at once propagated It will be noticed that a bar of wood is placed across the trough and that on the bar are two needle points neatly touching the surface of the mercury These points are a known distance apart and by measuri the negative Mr Vincent Vin-cent is abe to find the scale of reduction reduc-tion of the ripple lengths above the line a result which of course is only of jnteret to the physicist The second illustration shows us another an-other series of ripples so manipulated as to take a certain direction It is one of great beauty and in it we can trace the gradual enlargement of the waves as they recede further and further away from the point of disturbance Fig 3 shows the sets of ripples produced produc-ed by two tuning forks one malting 12S vibrations a second and the other 112 Then the two forks are said to pioduce i 16 beats a second The reason why tyr Vincent wished to set up two sets of ripples in the mercury was to illustrate illus-trate what is known as the interference interfer-ence of light When waves iwhethei in water or sound heat or light waves i mutually act upon one another their vibrations are increased diminished and neutralized and these phenomenn are classed under the term interference interfer-ence The interference of sound waves i I J1 iL i 11 f I L fL ViewofApparatusWithWhich the Ripple Photograph Are Taken 1 1 i and the consequent production of beats I is a well known lecture experiment i The color of a goalJ hubble or a stagnant j stag-nant pool are also illustrations of the j I interference of light I Thus in figure w e get an effect of 1 the mutual interference of one set of j ripples on the other Tht < urved light lires represent the places where the I ritst of one rlpnle exactly neutralizes 1 t1 trough ot another ripple Were we j dealing with bound waves we should have at these places what arc known i as rests if with light waves what are known as darkness and at other really color as inthe case of the soap hubble hub-ble shining in the sun j In figure 4 Mr VIncent has employed i a pointsource and a reflecting line j The former is the style attached to a tuning fork with a frequency of 180 I beats to a second while the latter is aside a-side of a triangular piece of microscope cmering kept in position by a small splinter of wood We see here a great I t many interference lines These dim and blurred lines are due to the mutual action of the primary and reflected I waves This photograph may help us to realize the reflection of sound waves in air We know that in order to hear all the sound produced the listener J opght to bo in full view of the orchestra orches-tra because some sound waves are unable un-able to come round corners and are re llected away from the listener who is situated behind some obstacle I CURIOSITIES OF WAVE MOTION j I Marc ni waves are endowed with j I such wonderful properties that they i arc able to go through brick walls and j round all sorts of corners Roentgen ray waves again can go through a great 1 many substances which are opaque to i ordinary light Waves In the fifth pho j I I tograph we have another instance of reflected mercury ripples fot Mr Vincent Vin-cent has here arranged a shallow circular j i I cir-cular reflector Weset at the corriers j 1 of this the samt blurred circles we sawn i saw-n another illustration attQ 6 t series of i i lenses are seen streaming away from i 1 the reflector The scientific mind calls 1 these confocal elipse and confocal j I hyperbolas but though the lay mind I cannot grasp the significance of these i I ripples I can at least appreciate the I beauty of the photographs and the ingenuity I in-genuity of the savant who took them I j Our sixth illustration shows the rip i pie breaking against a semicircular I reflector with mercury Tlje reflected J ripples take the curious shape of i straight lines in the middle but are i bent outward from the reflector toward I j to-ward the ends illustrating spherical aberration Number sever chow some queer pat i terns Instead of using the tuning I i fork and style of glass the ripples here j were originated by the agitation of d I slip of cover glass one side of which j is made to dip into the mercury they I I are reflected from the shallow circular mirror The interference effects are seen in the blurred waves at the bottom bllrred bojtom 1 of the picture and if the photograph be I carefully looked into many curious rip i I pie forms will be observed dueto reflection re-flection To students of natural philosophy I j phil-osophy these photographs should be iof great assistance in their study of i physical problems i The eight ant last picture gives usa us-a very interesting pattern The ripples i aif set up as in the previous photograph photo-graph and are reflected at an angle of about 45 degrees from a straight edge I The long black mark running from I I one end of the dipping tdge of the slip of covei glass to the corner ofthe print is due to a depression in the surface caused by a floating needle put thereto j there-to screen off the circular waves coming from the end of the strip of glass We I see to what straits the ripples are here put They cannot pursue the even tenor I of their way hut are so harassed by I obstacles that they take the most extraordinary ex-traordinary forms at which the mind II cannot fail to marvel In conclusion it may be said that I these photographs taken by Mr Vincent Vin-cent present analogues of the greatest service in demonstrating the phenomena I phenom-ena of acoustics and optics for they I are infInitely superior to geometrical pictures drawn by instruments We 1 have all been greatly interested in the I i wireless telegraphy experiments of Signor Marconi and others and we know that his invisible telegrams are carried by extremely rapid waves in the ether These photographs help us to realize how such things can be and the wave theory of light becomes clear I when we examine these mercury ripples rip-ples |