from simple trigonometrical calculations. At the Observatory of Montsouris, the degree of cloudiness, i. e., the amount of the whole sky covered with clouds at a given moment, is determined by means of the nephometer, also devised by Besson. This consists of a convex glass mirror, a segment of a sphere, about twelve inches in diameter, in which is seen the reflection of the celestial vault divided into ten sections of equal area by means of lines engraved on the glass. As shown in the front page engraving, the meteorologist observes through an eyepiece fixed in an invariable position with respect to the mirror, which latter turns freely on a vertical axis. The observer, whose own image partly obstructs sections 8, 9. and 10, notes the degree of cloudiness in the sections numbered 1 to 7. The cloudiness of each section is estimated on a scale of 0 to 10: zero meaning no clouds and 10 entirely overcast. The observer would then rotate the mirror and eyepiece 180 degrees and observes the cloudiness in sections 7, 5, and 2, which represent the regions of the sky that at the first observation corresponded to sections 8, 9, and 10. Grid nephoscope The grid nephoscope is a variation of the comb nephoscope, invented in Norway. Russian nephoscope Mikhail Pomortsev invented a nephoscope in Russia in 1894. References Meteorological instrumentation and equipment Russian inventions