Nicol prism

“ The most efficient agent discovered for the polarisation of light is that of Iceland spar, cut and mounted as a “Nicol” prism.
By cutting crystals of Iceland spar into two parts, at a particular angle, and cementing them together again in the reverse way, Nicol succeeded in showing that one of the two polarising pencils could be totally deflected to one side, while the other is directly transmitted through the Nicol prism, and thereby the beam of light becomes at once “polarised” in one plane only. ”

“ When the cloud texture has become sufficiently coarse to approximate to that of ordinary clouds, the rotation of the Nicol ceases to have any sensible effect on the quantity of light discharged normally.
The perfection of the polarisation, in a direction perpendicular to the illuminating beam, is also illustrated by the following experiments: A Nicol's prism, large enough to embrace the entire beam of the electric lamp, was placed between the lamp and the experimental tube. ”

“ Mesuré and Nouel’s Pyrometer.—This instrument, shown in fig. 62, consists of two Nicol prisms, between which is placed a piece of quartz cut perpendicularly to its axis. Light from the source, in passing through the first Nicol prism, is all polarised in the same plane; but on passing through the quartz is polarised in various planes, according to the wave-length. The colour seen after passing through the second prism, used as analyser, will depend upon the angle between this and [188] the first or polarising prism. The analyser is connected to a rotating disc, divided into angular degrees ”

“ When we place on the stage of the polariscope, the Nicols being crossed, a plate of a uniaxial crystal cut perpendicularly to the optic axis, and subsequently a similar plate of a biaxial crystal cut perpendicularly to that axis of the optical ellipsoid, either α or γ, which is the bisectrix of the acute angle between the two optic axes, and use the system of lenses which converges the light rays received from the polarising Nicol prism on the crystal, as shown in Fig. ”

“ With these prefatory theoretical remarks, which are necessary in order that the experiments now to 187be described should be understood, we may proceed to consider a graduated series of experimental demonstrations which it is hoped will render clear some of the more important features of crystal structure which have been dealt with in previous chapters. Our principal agent will be polarised light, that is, light which has been reduced to vibration in a single plane by means of the well-known Nicol’s prism. ”

“ We employ a pair of such Nicol prisms (a very large pair being shown in Fig. 71) , together with a convenient system of lenses for focussing either the object-crystal or the phenomena displayed by it, as a “polariscope,” which is the most powerful weapon of optical research on crystals which has ever been invented. When the two prisms are arranged so that the vibration planes of the polarised light which they would singly transmit are parallel, we speak of them as “parallel Nicols,” and 188light is transmitted unimpeded through the pair thus placed in succession ”

“ But as the sky-blue is gradually rendered impure by the growth of the particles — in other words, as real clouds begin to be formed — the polarisation begins to decay, a portion of the light passing through the prism in all its positions. It is worthy of note, that for some time after the cessation of perfect polarisation, the residual light which passes, when the Nicol is in its position of minimum transmission, is of a gorgeous blue, the whiter light of the cloud being extinguished. ”

“ If the grating be so placed that the bars (representing the planes of polarization) are perpendicular, the books can pass between them; while if the grating be turned round a quarter of a circle, they will become transverse, and the books cannot pass, while the shelves could do so. Carrying on this analogy, the tourmaline or Nicol’s prism polarizes the light by transmitting only those rays whose undulations are in planes parallel to the bars ”

“ Any means by which a beam of polarized light of large diameter—say 3 to 31⁄2 inches—could be obtained with all the convenience of a Nicol would be a real advance, for spar of sufficient size and purity for such a purpose has become so scarce and therefore so valuable that large prisms are difficult to procure at all. ”

“ As the Nicol is turned, the light seen laterally begins to fade; and when the instrument has been turned through a right angle, the only parts remaining visible are those which are reflected from the larger impurities floating in the water independently of the mastic. An effect still more beautiful, and at the same time more instructive, can be produced by interposing, as was done in the case of reflection, a plate of quartz between the Nicol and the medium which causes polarization. ”

“ All along the arc from the Matterhorn to Mont Blanc the light of the sky immediately above the mountains was powerfully acted upon by the Nicol. In some cases the variations of intensity were astonishing. I have already said that a little practice enables the observer to shift the Nicol from one position to another so rapidly as to render the alternative extinction and restoration of the light immediate. ”

“ The light which leaves the polarising Nicol is vibrating in one plane, but on reaching the crystal this is resolved into two rays vibrating at right angles to each other, and at 45° on each side of its previous direction of vibration, supposing the crystal to be arranged for the production of most brilliant colour. ”

“ Will you be equally lenient toward Nicol, should he be arrested and under your authority? Do you think you could do anything to help him? They say you are all powerful with your friends. Will you try to have Nicol’s punishment a little lighter? I don’t know what he has done, but 93don’t let them give him the knout, nor the dungeon, nor Siberia, nor anything. ”

“ One point only Nicol failed to recognise (at that date it is not surprising) , and in this lay the strength of his opponent's position: that the bedded structure, which apparently made such an important distinction between the so-called upper gneiss and that beneath the Torridon sandstone, was a structure, not original, but the result of these movements.
Nicol was popular with his pupils and friends. ‘His sturdy frame and indomitable strength of will bore him unharmed through countless geological journeys that would have overtasked the majority of men. ... ”

“ If the line of knobs represent the direction of a ray, their motions will represent the vibrations and waves to which the light is supposed to be due. In ordinary light these vibrations may take place in any directions perpendicular to the ray; and the effect of the crystal of which the Nicol is made, is to restrict these vibrations to a particular direction. In the arrangement now before you the first Nicol causes the vibrations to be altogether horizontal. When the second Nicol is placed similarly to the first, it will obviously have no further effect upon the light ”

“ On rotating the Nicol analyser the colours change, and appear at their maximum brilliancy when the field is dark and the Nicols crossed. Leaving the analyser crossed to the polariser, and rotating the stage and therefore the crystal, the colours again change, and at certain positions 90° apart during the rotation, marked by the two strong lines in Fig. 80, they disappear altogether, and the crystal becomes dark like the rest of the field, while the positions of maximum brilliancy of colour are found to be situated at the 45°-positions intermediate between these positions of “extinction.” ”

“ So he sends me to tell you that a car will be waiting at nine o’clock to-night outside the Cavalry Club. The driver will be a Hindu. You know what to say. Oh, my Nicol, my Nicol, go for my sake! You know it all! You are clever. You can pretend. You can explain you had no call. If you refuse—”
Nicol Brinn nodded grimly. “I understand! But, good God! How has he found out? How has he found out?”
“I don’t know!” moaned Naida. “Oh, I am frightened—so frightened!”
A discreet rap sounded upon the door.
Nicol Brinn crossed and stood, hands clasped behind him, before the mantelpiece. ”

“ From his own medicine chest he dispensed gratuitously to the indigent sick; and without fee he vaccinated all the children of the neighbourhood who were brought to him. After a short illness, he died on the 5th of November 1819. Of a family of three sons and three daughters, the eldest son predeceased him; two sons and two daughters still survive. The elder son, who bears his father's Christian name, is Professor of Civil and Natural History in Marischal College, Aberdeen, and is well known as a geologist. Mrs Nicol survived her husband till the 19th of March 1845. ”

“ Neil, he perceived, was already off for the shore, swimming hand over hand, as if a swordfish were after him. Nicol was being hauled up the side of the steamer at the end of a rope, just as he had been hauled up from the Eilean-na-Rona dungeon; and his brother Duncan had seized hold of the helm that had been cast loose when the boat went down. Satisfied that every one was safe, Rob himself struck out for the side of the steamer, and was speedily hauled on board, presently finding himself on deck with his two dripping companions. ”

“ Nicol came to me as soon as the meal was over, and together we sat down to consult.
"This is the Sabbath, your honour," said Nicol, "so ye may consider yoursel' free for the day at ony rate."
"Not so free," said I, for I knew my cousin Gilbert. "The men I've to deal with have no more respect for the Lord's day than you have for a Popish fast, so we must put that out of account."
"Weel, weel," said Nicol, "if that's sae it maun be sae. Will ye gang oot wi' him the day?" ”

“ Nicol at once guessed at what had happened, and ran instantly for the Priest. The good Father of Dounan was deeply skilled in medicine, as well as in divinity. He called for assistance, and antidotes were forcibly given to Murdoch Stewart, and passively received by his mother the Lady Stradawn. Their wretched existence was thus prolonged, though death could not be altogether averted. ”

“ Of course I do! I should know Nicol wherever I met him, whether in his old home or in the wilds of Siberia. He was younger when this was taken than when I knew him. He is an old man now.”
“Yes, very old,” the gendarme replied, sarcastically. “Forty-five, at least. Old enough to die, if he is not already dead.”
By this time my companions had crowded around the picture, commenting upon it and wondering where the original was, and how his portrait came into the possession of the Seguins. It was Mary, as usual, who asked direct questions. ”

“ Here was a new complication, with Nicol in it. I remembered the watch perfectly. It was bought at a jeweler’s in Ridgefield, who kept only the best wares. Nicol had seemed rather proud of it and consulted it frequently if the day was hot, the lessons hard and his pupils stupid and anxious to be free.
“And you suspect Carl Zimosky?” I asked, in an unsteady voice.
“Yes, we always suspect him. He is what you Americans call a bad egg—into one scrape as soon as he is out of another.” ”

“ Nicoll states himself to have seen this day, a youth of sixteen, a native of Aberdeen, who, having been born without power in his arms, either to eat or drink, or do any other thing for himself or others, ‘Almighty God, who is able to do all things, gave him power to supply all these duties with the toes of his feet, and to write in singular good legible and current write, and that with such haste as any common notar is in use to do. ”

“ Oh! let me go, Signor Nicolo."
"No," cried Nicolo, still on his knees, and tightly pressing the old gentleman's thin spindle-shanks together, "no, Signor Pasquale, I will not let you go until you give me your word that you will be present in my theatre the night after to-morrow. You need not fear any new attack! Why, don't you think that the Romans, once they have heard your work, will bring you home in triumph by the light of hundreds of torches? ”

“ Nigel was in hunting-costume, blithe and gay, with his precious armor and his small baggage trussed upon the back of a spare horse which Aylward led by the bridle. The archer had himself a good black mare, heavy and slow, but strong enough to be fit to carry his powerful frame. In his brigandine of chain mail and his steel cap, with straight strong sword by his side, his yellow long-bow jutting over his shoulder, and his quiver of arrows supported by a scarlet baldric, he was such a warrior as any knight might well be proud to have in his train. ”

“ Nicol, the author of "Halucket Meg," and other songs given in this work, was born at Inverleithen, Peebleshire, on the 28th of September, 1769, and died at the manse of Traquair 5th November, 1819, in the fiftieth year of his age. Having officiated as tutor in various respectable families, he eventually succeeded to the parish of Traquair in the year 1802, on the death of the Rev. Mr. Walker, whose sister he married. Mr. Nicol was a kind amiable man, and much respected by all who knew him; he had a fine appreciation of the beauties of nature, and marked human character with a keen eye. ”

“ Everything fell out even as Knolles had planned. As Nigel rounded the oak forest, there upon the farther side of it, with only good greensward between, was the rider upon the white horse. Already he was so near that Nigel could see him clearly, a young cavalier, proud in his bearing, clad in purple silk tunic with a red curling feather in his low black cap. He wore no armor, but his sword gleamed at his side. He rode easily and carelessly, as one who cares for no man, and his eyes were forever fixed upon the English soldiers on the road. ”