54 EINSTEIN'S "MASCHINCHEN" In their paper the Habichts pointed out the benefits of their instrument compared with quadrant electrometers. The most important advantages were the absence of an auxiliary battery, the solidity of its construction, and the low sensitivity to tempera- ture. They also proposed a different use for the machine as a generator of a constant electric voltage up to 1,000 V. In December 1911 Paul Habicht demonstrated the machine to the German Phys- ical Society. Einstein was pleased with his apparent success, writing a friend that "he [Habicht] has overcome resistance to the matter I believe that the little machine will soon have replaced sensitive quadrant and wire electrometers."[25] In fact, Ein- stein was overly optimistic about the invention, which never became popular. Prob- ably only a few were ever manufactured and sold, and the "Maschinchen" certainly never replaced precision electrometers, which were constantly being improved. The lack of popularity of the Einstein-Habicht machine has a number of causes. Even though the basic theory of the machine is quite simple, it is constructed in a relatively complicated way. Several undesired effects can influence its perfor- mance.[26] In addition, the output of the machine is easily influenced by electrostatic phenomena that are difficult to control. All electrostatic devices are strongly affected by atmospheric humidity as well as by dust. Moreover, electrostatic machines are of- ten self-charging.[27] Contact between different metals (for example the brushes and the metallic plates) or even contact between surfaces of the same material but with different physical properties can produce contact electricity.[28] In addition, friction between the moving and the static parts of the machine can generate very small quan- tities of electricity. In an electrostatic generator these phenomena can profitably be used for excitation, but in a multiplier intended for increasing and measuring very weak electric charges these effects are only detrimental. On the other hand, using the machine as a high-voltage generator (as proposed by Habicht) would not have been very practical. Physicists availed themselves of other and much more efficient and powerful instruments for this purpose. A firm founded by Habicht in 1927 sold the multiplier with a range of accessories such as special connections, an ionization chamber, an ultraresistor (for transforming the instrument in a current meter), and an electroscope[29] well into the thirties. One of these machines is now in the Physics Institute of the University of Tübingen.[30] Another one is kept in the physics cabinet of the Ingenieurschule of the Technikum Winterthur, Switzerland.[31] It was purchased in 1913 for 329 Swiss francs.[32] This particular multiplier, which is in very good condition, is only slightly different from the one described in the Habichts' paper. The difference is that the movement of the small electric motor is communicated to the rotating axle of the multiplier by a fric- tion wheel and not by a conveyor belt. Moreover, the metal box has a little protruding glass vessel which originally contained concentrated sulfuric acid to dry the air in- side the instrument, and the aluminum leaf electroscope can be connected to different stages of the multiplier.