operation, and adds one more to the list of sixteen cases so made out by foreign observers, and two by Dr. Fenwick, of England. In this instance the instrument deserves particular credit, as other methods had completely failed in the practice of competent observers.
This consists of a metal tube, about seven inches long, of a caliber of 22 French, having at the proximal end a funnel shaped ocular opening; at the distal, a short beak, similar to that of the catheter coudé. A window of rock crystal is set in the end of this beak, behind which a small electric lamp, controlled by a switch at the ocular end, is placed. A rectangular prism, the hypothenuse plane of which is silvered, is placed in the end of the straight portion of the tube, its superior face being seen just anterior to the angle formed by the beak. The distended bladder is illuminated by the electric lamp, the rays reflected from its wall falling on the prism experience total reflection, an inverted image being formed within the tube. The size of the field thus obtained is greatly increased by means of a telescope introduced into the tube. The image seen through the cystoscope is an inverted image, but right and left are not transposed.
THE CYSTOSCOPE.
There can be no question as to the great prospective value of the electro-cystoscope in diagnosis of many difficulties to which the bladder is subject. A variety of foreign bodies have already been reported as made out by use of this instrument. The locality, size, and color of vesical calculi have been demonstrated in my own experience. In one instance two stones were seen where only one had been previously found, but this of course might with care have been effected by means of the lithotrite. But it is in the diagnosis of the tumors, and encysted or impacted calculi, that the most essential service may be anticipated from the use of the cystoscope. The orifices of the ureters are quite readily brought into the cystoscopic field, and it is more than probable that (perhaps through the introduction of some clear fluid with which blood does not readily mingle—glycerine, for instance) the true source of a previously doubtful hæmaturia will be demonstrated.—Medical Record.
DISTANCE AND CONSTITUTION OF THE SUN.
So many queries about the solar system, or the members of it, have come recently to the attention of those in charge of this journal, from various sources, that it is thought best to make a brief statement of the present state of knowledge that astronomy has of the solar neighborhood in which we live.
Naturally we begin with the sun, and the oldest and most important problem which the study of this body offers is the determination of its distance from the earth in terrestrial units of measure. This distance is important because the knowledge of all the phenomena of all the heavenly bodies, except those of the moon, depend directly or indirectly on its value. The problem of the sun's distance is difficult because the data given for determining it are insufficient to enable the astronomer to apply the principles of trigonometry directly to it. He is, therefore, compelled to use indirect methods of solution, which, at best, give only approximations to the true distance, arising chiefly from small errors in observation, which, at the present time, seem unavoidable. A familiar illustration will make our meaning clear. The knowledge we have of the sun's distance depends on the accurate measurement of a small angle formed by drawing two lines from a point at the sun to the extremities of the earth's radius. That angle is called the sun's parallax. Ptolemy thought that this angle was 3′ of arc, but we now know that its value is very near 8.80" of arc, and that the error of this amount from the true angle probably is not more than 0.02". To measure this small angle has been the astronomer's great trouble since the time of Aristarchus, and he does not yet know its value accurately. His problem is like that of a surveyor attempting to measure a ball, whose real diameter is one foot, at the distance of 4.4 miles nearly; and unless he can determine the diameter of the ball so that he shall not be uncertain in his measure to the amount of 0.03 of an inch, his work will not add anything useful to present knowledge.
If we suppose the angle of parallax to be known, the computation of the distance of a celestial body is easy. Multiply earth's radius by 206,265 (seconds of arc in the unit radius), and divide the product by the angle of parallax in seconds of arc. The mean equatorial radius of the earth, as given in Clark's Geodesy, is 3963.3 English miles. The sun's distance for a parallax of 8.78" would be