by the contraction of the fibres at the roots of one portion of the ciliary processes while the other fibres are relaxed.

The design of creative Wisdom in varying the structure of the eye to the purposes to which it is to be applied is very conspicuous in the sheep. The muscle on the choroid coat is larger above than that which is below; its fibres take a different direction that it may more effectually compress the ciliary veins, and Petit's canal is broader allowing the crystalline more extended motion; in this manner enabling it more effectually to select its food and soon to watch against danger without lifting its head from the ground: or according to the degree of light, enabling it to remove the picture from the lucid tapetum to a part that is darker. The retina terminates where the muscle begins lest its action should interfere with the impressions received upon it. It is slit asunder in fishes apparently for no other purpose than avoiding the motions of the cord to which the triangular muscle is attached.

When we look from one object to another we are conscious of an effort and that some time is requisite for distinct vision; apparently allowing the vascular processes to be filled or emptied by compressing or not compressing the veins that return from them. The winding direction of the carotid before it gives off the ophthalmic artery, the smallness of the ciliary vessels and their bendings and anastamoses before reaching the processes prevent the blood from passing per saltum but conduct it in a steady uninterrupted course. In the cat an animal that has to watch her prey often for a very considerarble time, the artery that supplies the eye after making a curve, gives off a number of very small branches which make several convolutions before some of them again unite and penetrate the sclerotica. By this structure the eye may continue for a long time without losing its object. Momentary relaxation of the ciliary processes may be permitted without having again to bring the organ to the same focus.

That the theory advanced by Kepler and supported by Porterfield, that the eye is accommodated to different distances by the position of the crystalline nearer to, or more remote from the retina is the true one, and that the change is effected in the manner described is evident from the structure of the apparatus.

ART. III.-New mode of constructing the Mercurial Barometer; by J. L. RIDDELL, A. M., Lecturer on Chemistry.

THE design of this contrivance, is to render the indications of the barometer more obvious and delicate.

A C, is a vertical glass tube near thirty two or thirty three inches in length, as in the common barometer.

C D. An iron joint held together by screws.

GI. A horizontal glass tube five feet long, or of any required length.

A O. Torricellian vacuum. The mercury is continuous from O to P.

M K. A plumb line pendent in a glass tube, for adjusting the instrument so that CA shall be exactly vertical.

H. A spirit level, for detecting any variation of G I, from a horizontal direction.

The iron tubes serve in part as caps, into which the ends of the glass tubes are cemented; and at the places where the glass terminates, the iron must be so drilled that the corresponding calibres will be exactly equal and continuous. If the glass and iron are fitted accurately in the first place by grinding, a little resinous cement applied by heat, (such as shellac,) will render the junctions perfectly secure. That part of the iron tube which embraces the glass, may be attached with common cap cement. The iron faces that are pressed together by screws, should be accurately ground; and if the position of the instrument require it, pieces of thin leather may intervene. If the calibre of the ascending tube be one fourth of an inch, and that of the horizontal tube one fifteenth; the rise or fall of the mercury four fifths of an inch, will cause the horizontal column to move nearly a foot.

The same apparatus modified a little, becomes a very delicate air thermometer. It is only necessary that atmospheric pressure should be excluded, and that the tube GI should terminate at I in a bulb containing air. If the bulb be partly filled with the vapor of mercury, at the time it is sealed, the elasticity of the air within, will be of a low tension, when the instrument becomes cool. In this case the tube AC may be materially shortened, and the iron joint dispensed with. The vapor of water, alcohol or ether may be substituted for air, taking the precaution to leave an excess of liquid in the horizontal tube or bulb. An instrument of extreme delicacy, may thus be constructed, but whether air or vapor is used, it is rather more difficult to adapt a scale to it, than a common thermometer. Cincinnati, Ohio, April 8, 1834.

ART. IV.-Apparent Dimunition of Weight in certain circumstances; by W. E. A. AIKIN.

Sir David Brewster, in one of his letters on Natural Magic, addressed to Sir Walter Scott, relates the following "as one of the most remarkable and inexplicable experiments, relative to the strength of the human frame." The experiment was performed in the presence of Sir D. B. by Major H. who had seen it performed at Venice, under the direction of an officer of the American Navy. "The heaviest person in the party lies down upon two chairs, his legs being supported by the one and his back by the other. Four persons, one at each leg and one at each shoulder, then try to raise him, and they find his dead weight to be very great, from the difficulty they experience in supporting him. When he is replaced on the chairs, each of the four persons takes hold of him as before, and the person to be lifted, gives two signals by clapping his hands. At the first signal, he himself and the four lifters begin to draw a long and full breath, and when the inhalation is completed or the lungs filled, the second signal is given for raising the person from the chairs. To his own

* Mt. St. Mary's College, Emmitsburg, March 12, 1834. To Prof. Silliman.-Dear Sir-I send you the following as possibly possessing sufficient interest to find a place in the Journal of Science; if so, it is at your Respectfully and sincerely,

service.

your humble and obedient servant,

W. E. A. AIKIN.

surprise and that of his bearers, he rises with the greatest facility, as if he were no heavier than a feather. On several occasions I have observed when one of the bearers performs his part ill, by making the inhalation out of time, the part of the body which he tries to raise is left, as it were, behind. As you-have repeatedly seen the experiment and performed the part both of the load and the bearer, you can testify how remarkable the effects appear to all parties, and how complete is the conviction, either that the load has been lightened, or the bearer strengthened by the prescribed process. Major H. declared the experiment would not succeed if the person were placed on a board and the strength of the individuals applied to the board. He conceived it necessary that the bearers should communicate directly with the body to be raised. I have not had an opportunity of making any experiments relative to these curious facts, but whether the general effect is an illusion, or the result of known or of new principles, the subject merits a careful investigation."

Upon reading the above, my curiosity was sufficiently excited to induce a repitition of the experiments with a view merely to satisfy myself whether the whole affair was, as is above suggested, an illusion or an inexplicable fact. For this purpose and with the aid of some friends, the trials were varied and continued at different times, until all were satisfied "that the load had been lightened or the bearers strengthened by the prescribed process." As the results we obtain

ed may throw some light on the subject, I subjoin them for the curious. The "load" was represented by a young gentleman weighing about 120 lbs., who was placed on a table with the bearers, two on each side, so that they could respectively apply one hand to each shoulder and leg. The terms "more difficulty" and "more ease" refer to the exertion requisite to lift the load under ordinary circum

stances.

1st. Lifted simultaneously, by signal, without preparation to ascertain what resistance was to be overcome.

2nd. Repeated the first.

3rd. Used the method prescribed by Sir D. B., but not acting in unison, felt no relief.

4th. Repeated third, more successfully and evidently lifted with

7th and 8th. Lifted with the lungs kept inflated, and experienced more difficulty.

9th and 10th. Repeated fourth with same result.

11th and 12th. The bearers only used the prescribed method, the load took no part other than to give signals, result same as fourth trial. 13th and 14th. Having changed the load repeated first.

15 and 16th. Repeated fourth, same result.

17th and 18th. Repeated eleventh and twelfth, same result. 19th and 20th. Similar to fourth, except that the prescribed process was intentionally neglected by one of the bearers, unknown to the others, no difference in consequence was observed by the others, and but very little by himself. Except therefore, so far as the one bearer was concerned, the results were similar to that of the fourth trial. 21st and 22nd. Repeated fourth with same result. On these trials the load was placed on a board and the strength of the bearers applied to the board.

23rd. Repeated first, load still on the board.

24th and 25th. Same as twenty first and twenty second, same result.

26th, 27th and 28th. Load still on the board, repeated seventh and eighth with same results.

29th and 30th. Having changed the load, repeated the first. For this and the remaining trials, the load was kept on the board. 31st and 32nd. Repeated seventh and eighth, same result. 33rd. Repeated first.

34th and 35th. Repeated fourth, same result.

These trials were made at three different times with the assistance of three different parties. At each time it was found necessary after half a dozen trials, to intermit for a few moments, as the wrists of the bearers became quite tired. The following conclusions were &educed.

1st. When the lungs are fully inflated and the act of lifting and that of expiration is carried on simultaneously, the load is apparently lightened.

2nd. No other situation of the muscles of the chest will give the same result.

3rd. The result is independent of the co-operation of the person lifted and is equally perceived with an inactive weight and by consequence with an inanimate weight.