SYNOPSIS The paucity of solar radiation data is chiefly due to the lack of simple and portable instruments for direct readings. To fill this lack, there is described, under the name of “Solarimeter,” a combination of a thermopile (modified Moll type), closed hermetically, under a hemispherical glass cover, and directly combined with an electrical measuring apparatus of a simple millivoltmeter type. A system of two contact screws makes it easy to employ the solarimeter either for sun and sky observations on a horizontal surface or for pyrheliometric readings at normal incidence. For the latter a small pyrheliometric tube on a special holder is connected with the solarimeter box. All these new constructions should be considered as secondary instruments, which necessitate comparisons with normal pyrheliometers. Directions for using and testing the solarimeter are given, in which is emphasized the employment of a solar screen for determining the sky radiation by Doctor Kimball's method. A recording s... Abstract SYNOPSIS The paucity of solar radiation data is chiefly due to the lack of simple and portable instruments for direct readings. To fill this lack, there is described, under the name of “Solarimeter,” a combination of a thermopile (modified Moll type), closed hermetically, under a hemispherical glass cover, and directly combined with an electrical measuring apparatus of a simple millivoltmeter type. A system of two contact screws makes it easy to employ the solarimeter either for sun and sky observations on a horizontal surface or for pyrheliometric readings at normal incidence. For the latter a small pyrheliometric tube on a special holder is connected with the solarimeter box. All these new constructions should be considered as secondary instruments, which necessitate comparisons with normal pyrheliometers. Directions for using and testing the solarimeter are given, in which is emphasized the employment of a solar screen for determining the sky radiation by Doctor Kimball's method. A recording s...