I visited Lloyd’s laboratory a number of times after that，and found him always deep in his search after the absoluteblack. His experiments covered all sorts Of pigments， suchas lamp-blacks， tars， carbonized vegetable matters， soots ofoils and fats， and the various carbonized animal substances.
“White light is composed of the seven primary colors，”
he argued to me. “But it is itself， of itself， invisible. Onlyby being reflected from objects do it and the objectsbecome visible. But only that portion of it that is reflectedbecomes visible. For instance， here is a blue tobacco-box.
The white light strikes against it， and， with one exception，all its component colors—violet， indigo， green， yellow，orange， and red—are absorbed. The one exception is blue.
It is not absorbed， but reflected. Therefore the tobaccoboxgives us a sensation of blueness. We do not see theother colors because they are absorbed. We see only theblue. For the same reason grass is green. The green wavesof white light are thrown upon our eyes.”
“When we paint our houses， we do not apply color tothem，” he said at another time. “What we do is to applycertain substances that have the property of absorbingfrom white light all the colors except those that we wouldhave our houses appear. When a substance reflects all thecolors to the eye， it seems to us white. When it absorbsall the colors， it is black. But， as I said before， we have asyet no perfect black. All the colors are not absorbed. Theperfect black， guarding against high lights， will be utterlyand absolutely invisible. Look at that， for example.”
He pointed to the palette lying on his work-table.
Different shades of black pigments were brushed on it.
One， in particular， I could hardly see. It gave my eyes ablurring sensation， and I rubbed them and looked again.
“That，” he said impressively， “is the blackest black you orany mortal man ever looked upon. But just you wait， and I’llhave a black so black that no mortal man will be able tolook upon it—and see it！”
On the other hand， I used to find Paul Tichlorneplunged as deeply into the study of light polarization，diffraction， and interference， single and double refraction，and all manner of strange organic compounds.
“Transparency： a state or quality of body which permitsall rays of light to pass through，” he defined for me. “Thatis what I am seeking. Lloyd blunders up against theshadow with his perfect opaqueness. But I escape it. Atransparent body casts no shadow； neither does it reflectlight-waves—that is， the perfectly transparent does not.
So， avoiding high lights， not only will such a body castno shadow， but， since it reflects no light， it will also beinvisible.”
We were standing by the window at another time.
Paul was engaged in polishing a number of lenses， whichwere ranged along the sill. Suddenly， after a pause in theconversation， he said， “Oh！ I’ve dropped a lens. Stick yourhead out， old man， and see where it went to.”
Out I started to thrust my head， but a sharp blow onthe forehead caused me to recoil. I rubbed my bruisedbrow and gazed with reproachful inquiry at Paul， who waslaughing in gleeful， boyish fashion.
“Well？” he said.
“Well？” I echoed.
“Why don’t you investigate？” he demanded. Andinvestigate I did. Before thrusting out my head， my senses，automatically active， had told me there was nothing there，that nothing intervened between me and out-of-doors，that the aperture of the window opening was utterlyempty. I stretched forth my hand and felt a hard object，smooth and cool and flat， which my touch， out of itsexperience， told me to be glass. I looked again， but couldsee positively nothing.
“White quartzose sand，” Paul rattled off， “sodic carbonate，slaked lime， cutlet， manganese peroxide—there you have it，the finest French plate glass， made by the great St. GobainCompany， who made the finest plate glass in the world，and this is the finest piece they ever made. It cost a king’sransom. But look at it I You can’t see it. You don’t knowit’s there till you run your head against it.
“Eh， old boy！ That’s merely an object-lesson—certainelements， in themselves opaque， yet so compounded asto give a resultant body which is transparent. But that isa matter of inorganic chemistry， you say. Very true. But Idare to assert， standing here on my two feet， that in theorganic I can duplicate whatever occurs in the inorganic.
“Here！” He held a test-tube between me and the light，and I noted the cloudy or muddy liquid it contained. Heemptied the contents of another test-tube into it， andalmost instantly it became clear and sparkling.
“Or here！” With quick， nervous movements amonghis array of test-tubes， he turned a white solution to awine color， and a light yellow solution to a dark brown.
He dropped a piece of litmus paper into an acid， when itchanged instantly to red， and on floating it in an alkali itturned as quickly to blue.
“The litmus paper is still the litmus paper，” heenunciated in the formal manner of the lecturer. “I havenot changed it into something else. Then what did I do？ Imerely changed the arrangement of its molecules. Where，at first， it absorbed all colors from the light but red， itsmolecular structure was so changed that it absorbed redand all colors except blue. And so it goes， ad infinitum.
Now， what I purpose to do is this.” He paused for a space.
“I purpose to seek—ay， and to find—the proper reagents，which， acting upon the living organism， will bring aboutmolecular changes analogous to those you have justwitnessed. But these reagents， which I shall find， and forthat matter， upon which I already have my hands， will notturn the living body to blue or red or black， but they willturn it to transparency. All light will pass through it. It willbe invisible. It will cast no shadow.”