Response of highly precise balances to thermal gradients

As small thermal grad ients often cause large instabilities in t he i ndications of more precise balances, an investigation was made of the eff ccts of various types of t hermal gradients on several such ba lances. It was fo und that the largest instabiliLies resu lt when the Lop of the balance case is cooler t han the bottom, and f urther that the best p erfo rmance is obtained when air at the top is warmer, rather than in thermal equilibriu m throughout the case. The d esired thermal grad ients, i. e., top warmer than the bottom, can be achicved through proper insulation of the balance case, with provision for some flow of beat in through the lower front of the case a nd entrapment of warm air at the top of the case. TIl('se results apply directly to the equal-ar m type of balance; a separate stud y would bc required for balances of different configuration. However, the general nature of the effects of thermal grad ients is applicable to some degree to all types of more precise balances.