Marvels of Pond-life

n-Modes of stating magnified power-Use of an "Erector"-Power of various objectives with different eye-pieces-Examination of surface markings-Me

The most eminent English makers, Wales, and Tolles, in America, and Hartnack, in Paris, occupy the first rank, while the average productions of respectable houses exhibit so high a degree of excellence as to make comparisons invidious. We shall not, therefore, indulge in the praises of particular firms, but simply recommend any reader enteri

th the same object-glass; but only object-glasses of very perfect construction will bear the enlargement of their own imperfections, which results from the use of long tubes; and consequently for cheap instruments the opticians often limit the length of the tube, to suit the capacity of the object-glasses they can afford to give for the money. Such microscopes may be good enough for the generality of purposes, but they do not, with glasses of given focal length, afford the same magnifying power as is done by instruments of better construction. The best and most expensive glasses will not only bear long tube

isitors, who have been pleased with his microscopic efforts to entertain them. "Dear me, what a wonderful instrument; it must be immensely powerful;" and so forth. These ejaculations have often followed the use of a low power, and thei

, would be one hundred times one hundred, or ten thousand: and this is the way in which magnification is popularly stated. A few moments' consideration will show that the scientific method is that which most readily affords information. Any one can instantly comprehend the fact of an object being made to look ten times its real length; but if told that it is magnified a hundred times, he does not know what this really means, until he has gone through the process of finding the square root of a hundred, and learnt that a hund

sects, or of the exquisite preparations of entire insects, which can now be had of all opticians. Microscopes which have a draw tube can be furnished with an erector, an instrument so called because it erects the images, which the microscope has turned upside down, through the crossing of the rays. This is very convenient for making dissections

ds upwards. A new form, devised by Mr. Stephenson, acts as an erect

two thirds, from fifty to sixty diameters; a half-inch about one hundred; a quarter-inch about two hundred. The use of deeper eye-pieces adds very considerably to the power, but in proportions which differ with different makers. One instrument used by the writer has three

rent object properly placed, and the latter causes a number of rays to converge, producing a more powerful effect. The first is usually used in daylight, when the instrument is near a window (one with a north aspect, out of direct sunlight, being the best); and the second is often useful when the source of illumination is a candle or a lamp. By va

and down, should have an arm by which it can be thrown completely out of the perpendicular plane of the body of the instrument. This enables such oblique rays to be employed as to give a dark field, all the light which reaches the ey

rmaceti, and place them upon it, then put the whole on a piece of writing-paper, and hold it a few inches above the flame of a candle, moving it gently. If this is dexterously done, the spermaceti will be melted without singeing the paper, and when it is cold the disk will be found transparent. Place it over the hole in the diaphragm, send the light through it, and the result will be a very soft agreeable effect, well suited for many purposes,

ence is singularly convenient. It is high enough for many purposes, and can easily be raised by one or more blocks. A paraffine lam

ut a little practice to keep both eyes open, and only pay attention to what is seen by that devoted to the microscope. The acquisition of this habit is facilitated, and other advantages gained, by a screen to keep out extraneous light. For this purpose take a piece of thin cardboard about nine inches square, and cut a round hole in it, just big enough to admit the tube of the microscope, about two inches from the bottom, and equidistant from the two sides. Next cut off the two upper corners of the cardboard, and give them a pleasant-looking curve

one so deaf as those that won't hear," which naturally suggests for a companion, "None so blind as those that won't see." It is often impossible to get every object in the field in focus at one time;-look only at that which