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to be ruled within the width of an inch. All the parts of the machine by which a surface as hard as steel has thus traced upon it, by means of a diamond, a furrow several miles long, have to be made with extreme accuracy. A screw to rule a "grating" six inches wide required two years or more to make; and almost ten years were occupied in making one to rule a grating" fifteen inches wide. From beginning to end the process of producing a perfect optical grating is beset with difficulties, and only an indomitable spirit can overcome them. Nothing must be left to chance; and the slightest disregard of a possible disturbing influence during the grinding of the screw or the ruling of the grating means that months or years of work will be completely wasted.

Prof. A. A. Michelson, who devoted many years to the perfection of a machine for producing accurate optical gratings, has compared it to an antagonist who was always ready to take advantage of a mistake, yet always played fair.

One comes to regard the machine as having a personality —I had almost said a feminine personality-requiring humouring, coaxing, cajoling, even threatening! But finally one realises that the personality is that of an alert and skilful player in an intricate but fascinating game who will take immediate advantage of the mistakes of his opponent, who "springs the most disconcerting surprises, who never leaves any result to chance, but who nevertheless plays fair, in strict accordance with the rules of the game. These rules he knows, and makes no allowance if you do not. When you learn them, and play accordingly, the game progresses as it should. Prof. A. A. Michelson.

In order to test certain conclusions he had reached as to the effect of the earth's atmosphere in absorbing particular rays of sunlight, a French astronomer, Dr. Jules Janssen, wished to make observations at the

summits of high mountains, where the layer of air interposed between him and the sun would be less than at lower levels. He was lame, but that did not prevent him from attaining his object; he first ascended the Faulhorn, then the Pic du Midi, and afterwards undertook several ascents of Mont Blanc. His lameness made mountain climbing particularly difficult, and in order to reach the summit of Mont Blanc he had to be carried either on a litter or on a sledge. He not only achieved his original purpose, but created the observatory which now stands upon the snow of the very top of this famous peak of the Alps. The observatory is a monument to his energy and tenacity of purpose. Referring to the realisation of the project, he once said, "I have always thought that there are very few difficulties which cannot be surmounted by a will strong enough or by study sufficiently profound."

When Newton was actively engaged in completing one of his important works, a lighted candle which he left in his room burned down, setting fire to papers which represented the results of much labour, and destroyed them. The story of the fire having been caused by a little dog called "Diamond" upsetting the candle, and that the papers related to the famous Principia, is shown by Brewster to be fabulous. The fire did, however, destroy twenty years' work upon light and colour, which Newton had almost brought to a conclusion, and it was said at the time by a student at Cambridge, where Newton was a Fellow of Trinity College, everyone thought he would have run mad, when he had seen what was done; he was so troubled thereat that he was not himself for a month after." All that Newton himself said of the loss thus caused, when asked about it by a friend, was that he was obliged

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to work the calculations all over again. To have to reconstruct an intricate work from the very beginning. was sufficient to appal the strongest mind, but he set about the task and accomplished it.

The man who has the spirit of science in him is ever ready to sacrifice personal comfort or convenience to it. It is told of Dr. Robert Grant, who was professor of zoology in University College, London, and devoted to his subject, that he spent eight or ten hours of a sleety day in February wading in the shallows of the Firth of Forth, in order to secure some specimens of a certain small aquatic creature which can best be studied in a living state, as its beautiful and varied colours disappear when the animal is dead and immersed in spirit. When showing to his class the specimens he had obtained he said: "I had no companion, I had nothing to eat or drink, I was wet through, my hands were half frozen, and I was chilled to the marrow; but, gentlemen, I was amply rewarded; I became the happy possessor of no less than three of these beautiful little creatures, these Dorises," and he held up a phial containing three scarcely visible little bladder-like animals.

If there is one branch of science more than another in which the infinite patience of genius is required, it is that of the study of insects; not of insects pinned in boxes or arranged in cabinets, but of the living creatures, with the view of discovering something of their lifehistory or of understanding a type of mental life on lines different from ours. It is much more exciting to catch insects and to kill them with cyanide or chloroform, so as to convert them into specimens for a collection, than it is to watch their individual characteristics as living things, unravel the complicated thread of changes they undergo, and observe their domestic economy. On this

account there are many insect-hunters and collectors, but few who have an intimate acquaintance with the habits of insects in the life.

One such open-eyed naturalist was Réaumur, born at La Rochelle in 1683, and as diligent and accurate an observer as ever lived. Réaumur's History of Insects occupies six large volumes, and though issued so long ago as between 1734 and 1742 they are still a rich mine of information upon all aspects of insect-life observable with the naked eye or a simple lens. Referring to his accounts of the change from a caterpillar into a chrysalis, and of the chrysalis into a moth, Prof. L. C. Miall says : These luminous descriptions are now reproduced with cruel abridgment in all popular works which treat of insect-transformations. . . The only important additions which naturalists have made to Réaumur's account of the transformations of Lepidoptera relate to the internal changes, and these demand a minute acquaintance with insect anatomy."

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The geometrical or mechanical properties of Nature are far more easily defined with precision than are any of the processes of organic life. Five hundred years before the commencement of the Christian era, Pythagoras observed that the three angles of every plane triangle together make up two right-angles; and this conclusion stands now as it did then. Two and a half centuries later Archimedes proved that an object immersed in a fluid is buoyed up with a force equal to the weight of the fluid displaced; and this principle admits of no alteration whether it is applied to the flotation of a ship in water or the buoyancy of a balloon in air. Hipparchus, the founder of astronomical science, who lived in the second century B.C., determined the periods of revolutions of the planets with remarkable

accuracy, and his values differ very slightly from those accepted at the present day, but it was not until eighteen hundred years later that Newton discovered the law of gravitation by which the movements of these and other bodies in the solar system are governed.

An accurate observation remains unaltered throughout the ages. Its scientific value is determined by its truth to Nature; and the more complete the testimony, the less room is there for elaboration by investigators in succeeding generations. Whatever precise knowledge exists of natural things and operations has been obtained by patient labour. It is so much easier to accept traditional views upon the structure, habits and functions of the various forms of life around us than it is to inquire minutely into them by personal observation that mistaken ideas often pass currency for hundreds of years before they are detected. Aristotle in his natural history makes a king-bee the governor of a hive, and this view is reflected in Shakespeare's lines:

For so work the honey-bees,

Creatures that by a rule in nature teach
The act of order to a peopled kingdom,
They have a king and officers of sorts;

King Henry V. 1. ii.

It was a country parson, Charles Butler, who, in the early years of the seventeenth century, took the trouble to study bees themselves instead of reading books about them; and he found that the queen-bee was the dominant factor in the hive community. Milton possibly knew of Butler's work when he wrote in Paradise Lost, published half a century later, of "The female bee, that feeds her husband drone Deliciously, and builds her waxen cells With honey stored."