The fact that sun-spots wax and wane in numbers in a certain definite period was first ascertained by the amateur observer Schwabe of Dessau, whose work is a notable example of what may be accomplished by steadfast devotion to one particular branch of research. Without any great instrumental equipment, Schwabe effected the discovery of this most important fact--a discovery second to none made in the astronomical field during the last century--simply by the patient recording of the state of the sun's face for a period of over thirty years, during which he succeeded in securing an observation, on the average, on about 300 days out of every year. The period now accepted differs slightly from that assigned by him, and amounts to 11·11 years. Beginning with a minimum, when few spots or none may be visible for some time, the spots will be found to increase gradually in number, until, about four and a half years from the minimum, a maximum is reached; and from this point diminution sets in, and results, in about 6·6 years, in a second minimum. The period is not one of absolute regularity--a maximum or a minimum may sometimes lag considerably behind its proper time, owing to causes as yet unexplained. Still, on the whole, the agreement is satisfactory. This variation is also accompanied by a variation in the latitude of the spots. Generally they follow certain definite zones, mostly lying between 10° and 35° on either side of the solar equator. As a minimum approaches, they tend to appear nearer to the equator than usual; and when the minimum has passed the reappearance of the spots takes the opposite course, beginning in high latitudes. It has further been ascertained that a close connection exists between the activity which results in the formation of sun-spots, and the electrical phenomena of our earth. Instances of this connection have been so repeatedly observed as to leave no doubt of its reality, though the explanation of it has still to be found. It has been suggested by Young that there may be immediate and direct action in this respect between the sun and the earth, an action perhaps kindred with that solar repulsive force which seems to drive off the material of a comet's tail. As yet not satisfactorily accounted for is the fact that it does not always follow that the appearance of a great sun-spot is answered by a magnetic storm on the earth. On the average the connection is established; but there are many individual instances of sun-spots occurring without any answering magnetic thrill from the earth. To meet this difficulty, Mr. E. W. Maunder has proposed a view of the sun's electrical influence upon our earth, which, whether it be proved or disproved in the future, seems at present the most living attempt to account for the observed facts. Briefly, he considers it indubitably proved-- 1. That our magnetic disturbances are connected with the sun.