the white flint or crystal. He therefore ground a wedge of white flint of about 25°, and another of crown of about 29°, which refracted nearly alike; but their divergency of the colours was very different. He then ground several others of crown to different angles, till he got one which was equal, with respect to the divergency of the light, to that in the white flint; for when they were put together, so as to refract in contrary directions, the refracted light was entirely free from colour. Then measuring the refractions of each wedge, he found that of the white glass to be to that of the crown nearly as 2 to 3; and this proportion. would hold very nearly in all small angles. Therefore any two wedges made in this proportion, and applied together, so as to refract in a contrary direction, would refract the light without any difference of refrangibility. To make therefore two spherical glasses, that shall refract the light in contrary directions, it is easy to understand, that one must be concave, and the other convex; and as the rays are to converge to a real focus, the excess of refraction must evidently be in the convex; and as the convex is to refract most, it appears from the experiment, that it must be made with crown glass, and the concave with white flint glass. And further, as the refractions of spherical glasses are in an inverse ratio of their focal distances, it follows, that the focal distances of the two glasses should be inversely as the ratios of the refractions of the wedges: for being thus proportioned, every ray of light that passes through this combined glass, at whatever distance it may pass from its axe, will constantly be refracted, by the difference between two contrary refractions, in the proportion required, and therefore the different refrangibility of the light will be entirely removed. Having thus got rid of the principal cause of the imperfection of refracting telescopes, there seemed to be nothing more to do, but to go to work on this principle; but he had not made many attempts, before he found that the removal of one impediment, had introduced another equally detrimental (the same as he had before found in two glasses with water between them): for the two glasses, that were to be combined together, were the segments of very deep spheres; and therefore the aberrations from the spherical surfaces became very considerable, and greatly disturbed the distinctness of the image. Though this appeared at first a very great difficulty, yet he was not long without hopes of a remedy: for considering that the surfaces of spherical glasses admit of great variations, though the focal distance be limited, and that by these variations their aberrations may be made more or less, almost at pleasure; he plainly saw the possibility of making the aberrations of any two glasses equal; and as in this case the refractions of the two glasses were contrary to each other, their aberrations, being equal, would' entirely vanish. And thus at last he obtained a perfect theory for making object glasses, to the apertures of which he could scarcely conceive any limits; for if the practice could come up to the theory, they must certainly admit of very extensive ones, and of course bear very great magnifying powers. But the difficulties attending the practice are very considerable. In the first place, the focal distances, as well as the particular surfaces, must be very nicely proportioned to the densities or refracting powers of the glasses; which are very apt to vary in the same sort of glass made at different times. Secondly, the centres of the two glasses must be placed truly on the common axis of the telescope, otherwise the desired effect will be in a great measure destroyed. Add to these, that there are 4 surfaces to be wrought perfectly spherical; and any person, but moderately practised in optical operations, will allow, that there must be the greatest accuracy throughout the whole work. Notwithstanding so many difficulties, as here enumerated, after numerous trials, and a resolute perseverance, he brought the matter at last to such an issue, that he could construct refracting telescopes, with such apertures and magnifying powers, under limited lengths, as, in the opinion of the best and undeniable judges, who have experienced them, far exceed any thing that has been hitherto produced, as representing objects with great distinctness, and in their true, colours. XCIX. Of some Extraordinary Effects arising from Convulsions. By W. Watson, M. D., F. R. S. p. 743. In January 1757, Dr. W. was concerned for a young gentlewoman, who, if the number, continuance, and frequency of their returns, be considered, suffered the most violent and severe convulsions he ever knew. At some times the muscular spasms were general; at other times single muscles only, or a number of them, subservient to some particular purpose in the animal economy, were affected. And such was the peculiarity of this case, that after, and in proportion as any single muscle, or any determined number of muscles, had been in a stateof spasm, a paralytic inability succeeded to those muscles, which very much disordered and impaired, and several times even for no small continuance prevented the patient from performing several of her necessary functions. When the muscles, for instance, subservient to deglutition had been convulsed, for many hours after the fits had left her she had not been able to swallow a single drop of Iquid: so that when attempts had been made to cause her to drink, unless the liquor was immediately thrown back, there was imminent danger of her being strangled. When her eyes had been affected, several times a complete gutta serena, and total blindness, ensued; the patient being able to bear the strong day-light with open eyes, without being sensible of its influence, or in the least contracting her widely dilated pupils. After one of these fits the blindness continued full 5 days: and Dr. W. began to be in fear for the return of her sight. It is well known that vocification is performed in the aspera arteria; but that the articulation of sounds into syllables and words is modulated principally by the tongue, and muscles about the larynx. In this case, very early in the disease, the spasms seized the muscles about the larynx: the consequence of which was, that after they were over, the patient was unable to utter a word. This faculty however she again once recovered; but it continued a very short time, as the fits returned, which again left her deprived of the power of speech. After having lost her voice a second time, her power of speech did not return, even after she was freed from her convulsions, and her general health restored. Fourteen months passed, while this patient continued absolutely speechless; when, after having violently heated herself by 4 hours dancing, on a sudden her power of speech returned, and it has continued perfectly free ever since. What is still further remarkable in this case is, that during the whole time of this patient's continuing speechless, her life was rendered yet more uncomfortable by her having, from the injury to her brain by the spasms, forgot how to write, so as to express her meaning that way: but on the recovery of her speech, this faculty likewise returned, which she has retained ever since. During the severity of this disease, which continued several weeks, almost every day of which, from the number and violence of the convulsions, Dr. W. feared would be the patient's last, nothing was left unattempted, which he imagined could tend to prevent the return of the spasms, or lessen their effects. His endeavours so far happily succeeded, that her fits did not return; but the consequences of them continued, more particularly her inability to speak. After some months, however, when she was recruited in her strength, he was desirous of trying the effects of electricity, more particularly applied about her throat. This was accordingly attempted; but such was the state of her nerves, and their sensibility to its effects, that electrizing brought back the fits, which again affected her sight; so that he was compelled to desist, lest, in endeavouring to restore her speech, he might not only fail in this attempt, but might possibly bring on a permanent blindness. He determined therefore to trust the whole to time, which happily removed all her complaints. C. On an Extraordinary Storm of Hail in Virginia. By Francis Fauquier, This storm happened on Sunday the 9th of July, about 4 o'clock in the afternoon, and was preceded by some thunder and lightning. It was a small cloud that did not seem to threaten much before its breaking, and did not extend a full mile in breadth. It passed over the middle of the town of Williamsburgh, and the skirts of the town had but little of it. Its course was from N. by w. to s. by E. The hail-stones, or rather pieces of ice, were most of them of an oblong . square form; many of them an inch and a half long, and about three-fourths of an inch wide and deep; and from one side of most of them there proceeded sharp spikes, protuberant at least half an inch. He says he cooled his wine, and froze cream, with some of them the next day; and they were not totally dissolved when he went to bed on Monday night. This storm broke every pane of glass on the north side his house, and destroyed all his garden things entirely. He mentions likewise the heats as having been rather more than usual in that country this summer; and particularly on the 9th of August his thermometer (which is hung on the outside of his house on the north aspect) was at 97, by Fahrenheit's graduation, and some other days as high as 94 or 95. CI. An Extraordinary Case of a Diseased Eye. By D. P. Layard, M. D., F. R. S. p. 747. In October 1755 Dr. L. communicated to Dr. Maty, and he inserted in the last vol. of his Journal Britannique, the case of Susannah Earle, who, in consequence of the hooping cough, was afflicted with a protruded eye. The present case is somewhat similar to that girl's in its first appearance and progress, but by accident attended with a 2d disease. eye. John Law, a robust lad, 13 years old, in Easter week 1756, beating dung about a close with unusual force, on a sudden felt a violent pain in his left The pain increased, an inflammation ensued, and the eye grew daily larger. The poor boy's mother after several unsuccessful applications, brought her son, Oct. 7, to Mr. Daniel Hopkins, surgeon, in Huntingdon; and having desired Dr. L.'s opinion, both examined the eye together. The left eye was protruded out of its orbit, and hung down over the cheek to the upper lip. The coats were greatly discoloured, all the vessels turgid, the sight totally lost, and the humours appeared like fluctuating pus. They saw the necessity of an immediate extirpation, to save the right eye, already greatly inflamed; and having apprized the mother and boy of the state the eye was in, a consultation was desired with 2 surgeons of St. Ives; accordingly Mr. Skeeles and Mr. Want very charitably met Mr. Hopkins and Dr. L. the next day. On Mr. Want's pressing with his finger on the pupil, the globe burst at the edge of the iris, and discharged pus. The extirpation of the eye was unanimously agreed on, and immediately performed. Mr. Hopkins made a puncture with a lancet close to the external and small canthus of the eye, and then with a pair of crooked scissars took off all the distended globe close to the eye-lids. He then cleaned the cavity of the purulent humours, and filled it with soft lint, over which he applied bolsters dipped in warm red wine and water, and the monoculus bandage to keep on the whole dressings. The lad was bled in the arm; nitrous medicines and anodynes were prescribed, and a suitable regimen. The fever and inflammation of the eye gradually decreased; the suppuration of the wound in a few days was good, the distended eye-lids contracted, and a cure was soon expected. But on Nov. the 7th the lad went to open the street-door, and it being a cold and rainy evening, he quickly felt the bad effects of the cold wind, which drove the rain in upon him. That night the wound became again very painful, the eye-lids puffed up, and next day appeared much inflamed, as were all the contents of the orbit. Fungous excrescences soon followed, and an intermittent fever. An emetic being improper, he was purged with rhubarb, and afterwards took the bark infused in red wine. The fever was removed after some time; but the contents of the orbit continued increasing, and the fungous excrescences became so large and spongy, as to be of equal bulk with the diseased eye before extirpation. All topical applications, to contract this fungus, were ineffectual, and the application of caustics or escharotics was prudently avoided, lest they should produce a carcinomatous ulcer. The discharge was chiefly a purulent serum: on which account, ever since the beginning of November he was kept on a dry diet. In February 1757, the remaining coats of the eye began to appear at the most prominent parts of the excrescence, and seemed white like a part of the conjunctiva. On touching it with the finger, a distinct fluctuation was felt, and an hydrophthalmia perfectly discovered; but neither the thickness of the coats, nor the sensibility of the parts, would permit a puncture to be made, till the cyst, which appeared formed by the distension of one of the coats of the eye, was more free from the fungus. The cyst continued daily to extend itself, and to separate the fungous edges; the fluctuation became more manifest, and the membranes thinner. At length on the 15th of June, Mr. Hopkins opened the cyst with the point of a lancet, and let out a large cup-full of limpid serum, without smell or taste. The boy felt very little pain in this operation. The cavity was filled with dry lint, and compresses dipped in. warm red wine and water were applied over it. All the night following, and several days after, a great discharge of serum came away. On the 19th the fungus was considerably lessened. Mr. Hopkins then dressed: the wound with warm unguentum é gummi elemi, and washed the fungus with. a lotion of aq. calcis, ros. et tinct. myrrhæ. On the 23d, on his removing the dressings, he saw the cyst loose and collapsed; which he extracted with his forceps, without the least difficulty or pain to the patient. The fungus daily wasted afterwards, the wound digested well, and the lad was entirely cured on the 7th of August, The right eye became perfectly strong, and he continued free from complaint The remainder of the coats of the eye, and of the muscles, bore up the eye-lids, that when uncovered he only seemed to have closed the left eye: however, he |