96 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ON THE WET AND DRY BULB THEEMOMETEE. 



One of the most serious defects in the nse of the August 

 Psychrometer, or the wet and dry bulb thermometer, is due 

 to the fact that the radiation from surrounding objects af- 

 fects the covered thermometer quite differently from its ef- 

 fect upon the naked. In order to remedy this defect, Over- 

 beck, of Batavia, proposes to place the instrument within a 

 shelter formed of thin upright sheets of metal, so that the 

 direct rays of the sun can not strike the instrument. Metal 

 has some advantages over the wooden screens usually em- 

 ployed. Tijdschrift Voor JSfederlandsch Indie^ Batavia^ 1874, 

 120. 



PERIODICITY OF THE AUEOEA. 



Professor Fritz, whose great catalogue of all known auro- 

 ras was published in 1873, has recently communicated to the 

 Natural History Society of Zurich an investigation into the 

 relative periodicity of auroras and solar spots. He finds the 

 differences between the years of greatest auroral and sun- 

 spot frequency are sometimes positive and sometimes nega- 

 tive; but in general the maximum of the auroras occurs seven 

 tenths of a year after the maximum of sun-spots, while the 

 minimum of auroras occur three tenths of a year before the 

 minimum of the sun-spots. These differences, however, are 

 too uncertain to be spoken of as a definite law. As regards 

 the greater period of 55 years, he concludes that for the 

 present we can not improve upon the determination made 

 by himself in 1865, when he showed that this periodicity 

 could be best represented by assuming that it coincided with 

 five of Wolf's 11-year periods, or 55.55 years. He considers 

 it also probable that there is a still longer period of 222 

 years in auroras, which, of course, we are unable to detect 

 in the solar spots for want of observations. Vie?i?ia Zeit- 

 schrift fur Meteorologie^ X. , 3 1 7. 



THE NEW PHYSICAL OBSEEVATOEY NEAE ST. PETEESBUEG. 



Dr. Wild, of St. Petersburg, Director of the Physical Cen- 

 tral Observator}'-, gives an account of the establishment near 

 St. Petersburg, at the well-known summer resort Pavlosk, of 

 an auxiliary observatory, at which it is hoped numerous in- 



