WE have received a small portable sundial of ingenious construction, made of aluminium (“Kosmos-Sonnenuhr”. Stuttgart: Franckhesche Verlags-handlung). The workmanship is neat and attractive, and the instrument should be of value in giving instruction to schoolchildren. Some features call for comment. The sundial can be adapted to work in any latitude by rotating one of its members about an axis, the latitude being read off by a pointer against a scale marked from 0° to 90° by steps of 5°. This device, of course, helps the manufacturer to bring out sundials for various latitudes by mass production, and it may conceivably assist a teacher demonstrating fundamental principles to students; but we cannot imagine any real use for a sundial which is to be carried from one latitude to another. A further comment should be made on the method of adjustment in azimuth. A small magnetic compass is embodied in the instrument, and values of the magnetic variation for a number of places are given in the instructions. But if the instrument is to be set up permanently, one had better look up the equation of time in an almanac and set the instrument by adjusting it to give the right time, known independently. It will then, of course, work correctly; and this method of adjustment is easier to effect as well as being more accurate than the use of a tiny compass, liable to gross error through stray magnetic field.