Locomoteurs on Common Roads.

"MR. Goldsworthy Gurney has now contracted with wealthy and influential parties to build Steam-carriages for the road between Plymouth and Devonport; these parties have entered upon the speculation with a view to extend, hereafter, their operations on a much longer line."—Gordon, Treatise on Elemental Locomotion. May, 1836.

Railroad Acts, present Session, (May 25th incl.)

THE following Railroad Bills, in addition to No. 1 (see p. 275), received the royal assent on May 19th ;-2. Arbroath and Forfar; 3. Great Western Railway Act Amendment; 4. Birmingham and Derby; 5. Ulster; 6. Dundee and Arbroath; 7. Bristol and Exeter; 8. Aylesbury; and, 9. Bolton and Leigh, on May 20th.

Patent Law Grievance. No. III.

THE penalties inflicted on the inventive genius of Britain during the present year, up to the 26th ult., in the shape of government stamps and fees on patents, amount to more than £17,000!

N.B. This sum has been paid in ready money, on taking the first steps, and as many of the inventors are poor men (operatives), and a great many others of them persons to whom it would be very inconvenient to pay at least £100. down, they have been obliged to go into debt, or mortgage or dispose of their inventions, either wholly or in part, &c.

Hope Deferred.

We mentioned, p. 213, that Mr. Mackinnon had given notice in the House of Commons, on the 21st of March, that he should move for a Committee on the amelioration of the Patent Law on the 21st of April; from the 21st of April he deferred it until the 19th of May; from the 19th of May he has deferred it until the 14th of June!

NEW PATENTS. 1836.

ENGLISH.

N. B. The first Date annexed to each Patent, is that on which it was sealed and granted; the second, that on or before which the Specification must be delivered and enrolled.-The abbreviation For. Comm., signifies that the invention, &c., is "a communication from a foreigner residing abroad."

METEOROLOGICAL JOURNAL FOR APRIL, 1836; KEPT AT BLACKHEATH ROAD.

Barom.

Ther.
3 P.M.: attch. Min.

Day of Month

Barom.

Ther

Thermometer

9 A.M. attch.

Ther. Max. 58°9 on the 22nd. Ther. Min. 27°8

30th.

Lowest point of Rad. 26°, on the 30th. Rain fallen 3.040.

THE

MAGAZINE OF POPULAR SCIENCE,

AND

JOURNAL OF THE USEFUL ARTS.

RECENT RESEARCHES ON LIGHT.

Few branches of science have undergone a more entire renovation of late years, than that which relates to the phenomena presented by the subtile and mysterious agent, light, and the theoretical views by which those phenomena may be explained.

It is a somewhat remarkable feature in the history of physical optics, that the most complicated appearances which experiment exhibits, are, in many instances, among those which are the most perfectly understood, and explained on mathematical principles; whilst some of the simplest kind, and which are everywhere familiar to us, are among the number of those which have long remained without illustration; and, even now, have scarcely received any complete elucidation. There are few parts of the subject in reference to which the above remark has been more strikingly exemplified, than the phenomena and theory of prismatic dispersion.

In attempting a popular sketch of the most important points of recent investigation connected with this curious branch of science, we shall find it necessary to offer a few preliminary illustrations of the nature of prismatic dispersion; especially, as it is a point on which, even among scientific men, very vague and imperfect conceptions have often. prevailed.

REFRACTION AND DISPERSION.

THE ancients succeeded in perfectly tracing the law and consequences of the reflection of light; the law, indeed, was so simple, (viz., that the angle of reflection is always equal to that of incidence,) that to the mathematicians of antiquity, it held out an inviting field for the application of geometrical skill; which was early employed for tracing a variety of theorems resulting from that law, and when the first physical principle was established, the whole of " Catoptrics," was little more than a continued exercise of geometrical deduction from them. Not so with " Dioptrics," or the investigation of the course and properties of transmitted light. It was long, in this case, before the very first principle was discovered.

That a ray of light, entering obliquely out of a rare medium, as air, into a dense medium, as glass, or water, bounded by a plane surface, deviates from its previous rectilinear course, and takes a new, but still rectilinear, path within the new medium, was observed as the funda mental fact of dioptrics, long before any theory was imagined, by which it could be accounted for. What particular direction it would take under particular circumstances was also a subject of inquiry: and it was early observed, that if a perpendicular to the surface be imagined drawn at the VOL. I. 6

2 B

point where the ray falls upon it, its course will still continue in the same plane, but its deviation in direction will be of such a kind that it falls nearer to the perpendicular than it did before.

1.

In the annexed sketch the ray r, falls upon the plane surface of the dense medium m, and takes a new course r', nearer to the perpendicular p, that is, forming a less angle ' with it, than that which it formed before, . Observers for a long time could not discover anything in the way of a more precise relation, or law, than this. At length, however, upon the comparison of a number of observations, it appeared that the new angle (which is called the angle of refraction, as is called the angle of incidence,) always bears a certain relation in magnitude to 4, and that its actual amount varies very considerably in different substances. In any one medium the angles are not simply proportional one to the other, but bear a somewhat more complex relation, which is expressed by the trigonometrical law that their SINES are in a constant ratio. This law was discovered by Snell, (1619,) and is the foundation of optics. The absolute value of the constant ratio is different for different media, and is called" the refractive index" of the medium. When the ray of light arrives at the second surface of the medium, precisely the same thing takes place in reverse order. Thus, if the surfaces be inclined to one another, the ray will undergo a new deviation at the second surface, which may augment its entire deviation from its original course. This will be evident by looking at the course of such a ray traced in the annexed figure 2, where the successive angles are marked ' " q′′ and m is a dense transparent medium surrounded by air. Now this medium m, with inclined surfaces as here represented, obviously forms a portion of a triangular prism, and the deviation which a ray undergoes is thus magnified by its passage through two inclined surfaces, so that by this means we have the best experimental method of measuring the effect of refraction in different media.

o

Φ

But it was soon found, especially by this last mode of observation, that besides deviation another phenomenon is produced: viz., colour; that is to say, that if a ray of ordinary white light enter a dense medium, it is separated into certain component parts, which give sensations of different colours: this is the case in a very small, indeed quite insensible degree, at one refraction, but in two at inclined surfaces, as in fig. 2, it becomes perfectly conspicuous. The progress of the effect is represented in fig. 3,