142 PRACTICAL INSTRUCTIONS IN THE ART OF PHOTOGRAPHY. latent or hidden, the same as caloric or PRACTICAL INSTRUCTIONS IN THE heat, and enter into combination with ART OF PHOTOGRAPHY. CHAPTER IV. LIGHT AND ITS PROPERTIES. COLOUR AND OTHER PECULIARITIES OF BODIES DUE TO LIGHT DECOMPOSITION OF A SUNBEAM-FRAUNHOFER'S SPECTRAL PHOTOGRAPHIC 14. We have now to consider some of the properties of light, and therefore shall pass in review its leading characteristics. 15. Light is transmitted in all directions in straight lines (as in Fig. 5), and traverses about 192.500 miles in a second of time. Fig. 5. 16. When a beam of white light ($ 9, 10) falls upon the surface of any body, effects are produced varying with the body upon which it falls. Thus it may be absorbed, and disappear entirely; or be nearly all reflected or thrown back; or it may pass through the body, and it is then said to be transmitted; and, lastly, it may be partially absorbed, partially reflected, and partially transmitted. There are other effects produced by light; but as photographers do not require to know them, we must leave their consideration to those who wish to make the delightful science of Optics their study. 17. The colour of bodies is due to the absorption of light. A body that absorbs all the rays will appear black, while one that reflects them, will seem white; but some substances absorb some of the rays and reflect the others. A yellow surface reflects the yellow rays, and absorbs the others; a blue surface reflects the blue; a scarlet surface absorbs all the rays except the red. Light is the cause of colour in animals, plants, and minerals; but what becomes of the light that is absorbed by bodies is unknown: it may possibly be them, for it is evident that light may be extricated from some bodies without any change being produced, as in pyrophori or substances which absorb light, and emit it again when carried back into a dark place. The taste, odour, and combustibility of plants is due to the absorption of light; for a plant reared in the dark is nearly colourless insipid, inodorous, and possesses very little combustible matter, because plants exhale the carbon in the form of carbonic acid when in the dark, while they absorb carbon when in the light, and exhale oxygen gas. * 18. From what has been adduced before (§ 16), it is evident that light is decomposed by absorption, for when a beam of light fallupon a blue glass, the blue ray is separated from the rest of the rays of the spectrum and reflected, while the other rays are absorbed. Sir David Brewster instituted a very interesting series of experiments upon the conditions of the spectrum and its rays. but although willing to communicate hi views, we are unable on account of other matters of more importance to photographers. 19. One of the most curious effects of H the absorption of light is that which is discovered by examining the solar spectrum with a telescope. If this is done, numerous dark bands or lines (a representation of some of the larger of which is given in Fig. 6), are observed to be crossing the coloured rays. These bands, or lines, which are nearly 600 in number, are generally called Fraunhofer's dark lines, which have been demonstrated by Dr. Miller, the Professor of Chemistry in King's College, London,† to vary continually with the alteration of the atmospheric conditions. This fact, which should be remembered, is of importance to the photographer, as will be explained hereafter. These lines are not found in the spectra of ordinary artificial lights, although Fig. 6. F they are discovered in those of the sun and the planets. In the electric spectrum, the dark lines are replaced by brilliant ones, and the light is much clearer, so that we anticipate the day when the electric light will be used instead of the sun's light, with greater certainty, and perhaps more power, Electricity and photography are in their infancy. Therefore, who can foresee the benefits that will result to society, nay, to the universe, from the daily improvements in both sciences? Even now we are following out a series of experiments with the electric light in connection with Photography, that bid fair to cause a change in the art; and we hope before the present series is completed to lay the result before our readers.* 21. If we employ a convex surface to reflect from, instead of a plain one, the image will be reduced in size, and the outline be defective, because the imaginary, or virtual focus of reflection varies for different parts of the same figure, while the central portion alone is correct. This fact is most important, as we shall learn hereafter. 22. If a concave reflecting surface is employed, the image becomes inverted, or turned upside down. BEARDED CIVILIZATION. IT may not be generally known that beards are singularly connected in history with the progress of civilization. The early Greeks 20. If the same sunbeam that we ad- and Romans did not shave. The Greeks mitted into the room a short time before, began to use the razor about the time of and allowed to fall upon the prism (§ 10) Alexander, who commanded all his soldiers had been permitted to fall upon a polished to shave, lest their beards should afford a metallic surface, the rays would have been handle for their enemies. This was little reflected or turned into another direction, more than three hundred years before the so that the angle of incidence would have Christian era; and thirty years after Alexbeen exactly equal to the angle of reflee-ander, Ticinius introduced the habit or tion. The angle of incidence means the angle formed by the line in which the light moves in a straight line perpendicular to the plane. For example, if the direction of the incident beam (n in Fig. 7) be oblique to the plane (m i'm), or surface of the reflecting body, Fig. 7. m n then the beam will be reflected in such a direction (id) that supposing a perpendicular imaginary line pi) to be drawn between the incident beam and its reflection, the angle of reflection (dip) is equal to the angle of incidence (n ip); consequently it follows, that the beam makes the same angle with the perpendicular, both before and after its reflection. shaving amongst the Romans. The Gothic all the long controversies between the THE WORK-TABLE FRIEND. JEWELLED DESSERT MAT. Materials.-Messrs. W. Evans & Co.'s white of ingrain pink boar's-head crochet cotton, No. 10, 2 reels; and 1 oz. emerald beads, No. 2. BEGIN by threading all the beads on the cotton. Make a chain of four stitches, and close it into a round. 1st Round.-+ 1 Ch, 1 Sc on one of 4 Ch, 1 Ch + 4 times. 2nd Round.-+ 1 Ch, 3 Sc, coming on 1 Se, and a chain at each side, 1 Ch +4 times. On referring to the engraving, two diagonal lines, crossing in the centre of the mat, and dividing it into 4 parts, will be seen. All the increasing is done by making two chains at each of these corners, in every round of the mat, thus increasing 8 stitches in the entire round. For the sake of making the directions clear, we give these chains at the beginning and end of every quarter. The pattern is formed entirely of beads. 3rd Round.-+ 1 Ch, 5 Sc, 1 Ch +4 times. 4th Round.+ 1 Ch, 7 Sc, 1 Ch +4 times. 5th Round.-+ 1 Ch, 9 Sc, 1 Ch +4 times. 6th Round.-+1 Ch, 11 Sc, 1 Ch +4 time. 7th Round.-+ 1 Ch, 1 cotton, 2 beads. 1 cotton, 1 bead, 3 cottons, 1 bead, 1 cotton, 2 beads, 1 cotton, 1 Ch + 4 times. 8th Round. + 1 Ch, 2 cotton, 5 beads. 1 cotton, 5 beads, 2 cotton, 1 Ch +4 times. 9th Round.+ 1 Ch, 4 cotton, 1 bead, I cotton, 2 beads, 1 cotton, 2 beads, 1 cotton, 1 bead, 4 cotton, 1 Ch + 4 times. 10th Round.-+ 1 Ch, 4 cotton, 3 beads, 1 cotton, 3 beads, 1 cotton, 3 beads, 4 cotton, 1 Ch + 4 times. 11th Round.-+ 1 Ch, 6 cotton, 4 beads. 1 c, 4 beads, 6 c, 1 Ch + 4 times. 12th Round.+ 1 Ch, 9 c, 1 b, 1 c, 1b. 1 c, 1 b, 9 c, 1 Ch + 4 times. 13th Round.-+ 1 Ch, 8 c, 4 b, 1 c, 4 b. 8 c, 1 Ch 4 times. 14th Round.+ 1 Ch, 8 c, 3 b, 1 c, 3 b, le, 3 b, 8 c, 1 Ch + 4 times. 1 c, 1 b, 2 c, 5 b, 7 c, 2 b, 9 c,. 1- Ch + 4 times. 34th Round+ 1. Oh, 3c, I, 10 c, 15th Round.+ 1 Ch, 10 c, 1 b, 1 c, 2b, 1 c, 2 b, 1 c, 1 b, 10 c, 1 Ch+41 b, c, 4b, 3c, 4b, 3 c, 1 h, 4 c,. 1 b, times. 16th Round+ 10 c, 1 Ch 4 times. 17th Round Ic, 4-b, 4 c, 5 b,.6 c, 1 b, 10 c, 1 Ch + 4 ch, 10 c, 5 b, 1c, 5b, times. 1ch, 11 c, 2 b, 1 c, 1b, 3 c, 1 b, 1 c, 2 b, 11 c, 1 Ch + 4 times. 1 Ch, 35 c, 1 Ch + 4 18th Round 35th Round.+ 1 Ch, 5. c, 2 b, 10 c, 4b, lc, 1 h, 2 c, 4 b, 1 c, 1 b, 7 c, 4 b, 1 c, 1 b, 3 c, 5 b, 6 c, 2 h, 9 c, 1 Ch+4 times. 36th Round.+ 1 Ch, 7 c, 1 b, 2 c, 3 b, 6 c, 1 b, 1 c, 4 b, 3 c, 1 h, 2 c, 1 b, 2 c, 2 b, Ch, 1 b,. 3 C, b, 4 c, 1 b, 1 c,, 5 b, 3 c, 1 b, 9 c, b, 2 c, 13 c, 1 b, 4 G 1 b, 13 c, Ch+43 b, 5c, 1 Ch + 4 times. times. 19th Round.+ times. 20th Round.+ 1 Ch, 2 b, 1 c, 3 b, 10 c, 1 b, Lc, 2 b, 1 c, 4 b, 14 c, I bead on a chain stitch + 4 times. 21st Round.+ 1 Ch, 6 b, 2 c, 2 b, 1 c, b, 4 c, 2 b, 1 c, 6b, 1c, 2 b, 2c, 1b, 4c, 2 b, 1 Ch + 4 times. 22nd Round+ 1 bead on chain, 3 b, 2c, 1 b, 2 e, 1 b, 2c, 1 b, 3 c, 1 b, 1 c, 5b, 2 c, 1 b, 5c, 1 b, 2 c, 2 b, 5 c, 2 b, 1c, 1 bead on chain + 4 times. 23rd Round.+ 1 Ch, 1 c, 1 b, 2 c, 4 b, le, 1 b, 5 c, 4 b, 1c, 1 b, 2 c, 4 b, 4 c, 1 b, 7 c, 4b, 2 c, 1 Ch + 4 times. 24th Round.+1 Ch, 4 c, 4 b, 3c, 1 b, 2c, 1 b, 1 c, 4b, 3c, 4b, 6c, 1 b, 8 c, 5 b, 1 Ch 4 times. 25th Round.+ 1 Ch, 2 c, 5 b, 4 c, 2 b, 2 c, 4 b, 1 c, 1 b, 1 c, 4 b, 8 c, 3 b, 5 c, + b, 2 c, 1 b, 1'Ch + 4 times. 26th Round 1 Ch, 4 c, 4 b, 2 c, 2 b, ic, 2b, 1 c, 1 b, 4c, 4 b, 4 c, 3 b, 8 c, 2 b, 1c, 1 b, 4 c, 1 Ch + 4 times. C, 1 b, 3 b, 5 c, 27th Round.+ 1 Ch, 2 c, 6 b, 2 5c, 3 b, 3 c, 6 b, 4 c, 1 b, 12 e, 1 Ch + 4 times, 1 28th Round 1 Ch, 1 c, b, 3 c, 6 b, 3 c, 2 b, 1 c, 5 b, 3 c, 6 b, 13 c,, 3 b, C, Ch+4 times. 29th Round. +1 Ch, 4 c, 4 b, 1 c, 1 b, fc, 4 b, 1 c, 1 b, 4 c, 4 b, 2 c, 1 b, 4 c, 5 b, 11 c, 1 b, 5 c, 1 Ch + 4 times. 30th Round.+ 1 Ch, 5 b, 5 c, 2 b, I c, 5 b, 3c, 6 b, 4 c, 2 b, 2 c, 5 b, 13 c, 6 b, 1 Ch 4 times. 31st Round. +1 Ch, 3 c, 1 b, 6 c, 3 b, 3 c, 6 b, 2 c, 1 b,, 6 c, 3 b, 4 c, 7 b, 11 c, I b, 4 c, 1 Ch + 4 times. 32nd Round.+ 1 Ch, 2 e, 2 b, 8 c, 2 b, le, 1 b, 4 c, 4 h, 2 c, 2 b, 5 C2 2 b, 1c, 1 b, 5c, 5 B, 8 c, 2 b, 6 c, 1 Ch 4 times. 33rd Round.+ 1 Ch, I c, 2 b, 10 c, 4 b, le, 1 b, 1 c, 4 b, 5 c, 2 b, 3c, 4 b, 37th Round 7 c, 2 b, 1c, 6 b, 2 b, 1 c, 7 b, 9 c, +4 times. 1 b, 38th Round.+ 1 Ch, 15 c, 1 b, 8 c, Ic, 2 b, 1 c, 4 b, 5c, 1 b, 6 c, 1 b, 1 c, 2b, 1 C, 5 b, 13 c, 1 b, 6 C, 1 Ch + 4 times. 39th Round.+1 Ch, 14 c, 2 b, 12 c, 1 b, 4 c, 1 b, 4 c, 1 b, 10 c, 1 b, 5 c, 1 b, 11 C, 2 b, 8 c, 1 Ch + 4 times. 40th Round. All cotton, increasing as usual at the corners. 41st Round.-A bead on every stitch. BORDER, in which a bead is dropped in every stitch, whether Ch, Se, or Dc. 1st Round.+ 1 s, 5 Ch, miss 4 + all round, except at corners, when miss 2. 2nd Round.-5 De on centre of 5 Ch, + 4 Ch, 1 Se on centre of next 5 Ch, 4 Ch, 5 Dc on centre of next 5 Ch + all round. LADY'S NIGHT-CAP, IN CROCHET. Materials.-6 reels of Messrs. W. Evans and Co.'s Boar's-head Crochet Cotton, No. 24. THE wish expressed by many of our subscribers that we should furnish them with a pretty pattern for a night-cap in crochet, has induced us to give them one which we think they will find to be equally comfortable and becoming. THE CROWN.Make a chain of 73 stitches. 1st Row.-Miss 1, 2 Sc, + 4 Ch, miss 3, 1 Dc, 4 Ch, miss 3, 3 Sc, + 6 times. The seventh time end with I Sc, 1 De, 1 Tc. Turn the work. 2nd Row.-3 Ch, Dc on the Dc, 4 Ch, + 2 Sc, under the first chain of 4, 1 Sc on 1 De, 2 Sc, under the next chain of 4, 7 Ch, +7 times. De on the 1st chain of previous Ꮮ the+is merely to increase gradually the width of the crown. 3rd Row.-Turn the work. 3 Ch, Dc on the Tc; 4 Ch, 2 Sc under Ch, 1 Se on Dc, 2 Sc under Ch, +6 Ch, De on centre of 5 Sc, 4 Ch, 3 Sc under chain of 7+ to the end, at which increase a little. Repeat the 2nd and 3rd rows twice more, increasing a little at the end of every row, and then do the 2nd row only, still increasing. Observe the Tc stitches always come exactly over each other. Next Row (9th).-7 Ch, 5 Dc under the 4 Ch, 3 Sc over Sc, +10 De under chain, 3 Sc on centre of 5 to the end. Finish to correspond with the beginning. 10th Row. Turn the work. 3 Ch, miss none, 4 Se on nearest 4 Dc, + 6 Ch, 3 Se on centre 3 of 10 Dc +. Repeat to the end. After the last Sc, 4 Ch, Sc on 4th of 7 Ch at the beginning of the last 11th like 3rd, but begin with 3 Sc under Ch of 4. Continue increasing till further orders. 12th like 2nd. 13th like 9th. 14th like 10th. 15th like 3rd. 16th like 2nd. 17th.-5 Ch, Sc under Ch, 5 Ch, miss 3, 1 Sc, +5 Ch, Sc under Ch, 5 Ch, Sc on 1st Sc, 5 Ch, Sc on last Sc, + to the end. HE TRO Do 2 Sc (with a chain of 5 between) at the end of the row. LADY'S NIGHT-CAP IN CROCHET, BY MRS. PULLAN. row, 4 Ch, Tc on the missed stitch at the beginning of first row. The work after 18th. 5 Ch, Sc under Ch + repeat to the end, doing it twice in the last stitch. 19th, 20th, like 18th. 21st. 5 Ch, Sc under chain+ 4 times *, 5 Dc on Sc of last row, Sc under the next chain † 5 Ch, Sc under Ch† 7 times Repeat between the stars to the end. Increase as usual. 22nd like 18th. When you come to the 5 Dc, do a Sc under the centre one, instead of under the chain as in the other parts. |