SKETCH OF PROFESSOR MAYER. 231 



described ia a paper in the American Journal of Science and Arts, 

 entitled "A New Apparatus for the Determination of Carbonic 

 Acid," which was republished in Germany. His second paper was 

 on the estimation of weights of very small portions of matter, in 

 which he showed that, by the deflections of fine glass fibres, we can 

 weigh a particle of matter as small as the T qV 0" f a milligramme. 

 While at the Lehigh University, he designed and superintended the 

 erection of an astronomical observatory, put together and adjusted 

 the instruments, and made a series of observations on the planet 

 Jupiter, which were republished in England. He was in chai-ge of 

 the party sent by the United States Government to observe the 

 eclipse of the sun at Burlington, Iowa, August 7, 1869, and took 

 forty-one perfect photographs of the eclipse with exposures lasting 

 only the -g-JoOf a second. 



While at the Lehigh University, Prof. Mayer contributed to the 

 American Journal of Science and Arts and the Journal of the Franklin 

 Institute various original contributions on the " Solar Protuberances," 

 " Spectral Analysis of the Stars," " Physical Constitution of the Sun," 

 " Electro-Magnetism," " Electric Conductivities," " On the Alleged 

 Electro - Tonic State," "Magnetic Declination in Connection with 

 the Aurora," " Photographing the Magnetic Spectra ; " and at the 

 Salem meeting of the American Association he read an instructive 

 paper " On the Thermo-Dynamics of Waterfalls." He had taken the 

 temperatures of the water at Trenton and Niagara before it leaps the 

 cataract and after it strikes below. According to theory, when the 

 falling motion is arrested, it is converted into heat, and should be 

 shown in a rising temperature below. The observations indicated 

 that the effects of evaporation and contact of the divided water with 

 the air were greater than the impact in changing the temperature 

 of the fallen water, so that it may be actually colder below than 

 above. But on days when the air is saturated with moisture, and the 

 temperatures of the water and air are about the same, results were 

 obtained which show that the warming of the falling water conforms 

 to Joule's law of the conversion of motion into heat. 



Since entering upon his duties at the Stevens Institute of Tech- 

 nology, notwithstanding the labor of lecturing and teaching which 

 the position involves, Prof. Mayer has conducted elaborate investi- 

 gations in various branches of physics, which have given to science 

 many new and important results. Among these may be mentioned 

 researches in magnetism, heat, and especially " On the Effects of 

 Magnetization in changing the Dimensions of Iron and Steel Bars," 

 and " On the Isothermals of the Solar Disk." We cannot here give 

 the particulars of these interesting inquiries, but must refer the reader 

 to the memoirs in the scientific journals. 



The line of investigation, however, to which Prof. Mayer has 

 mainly devoted himself within the last few years is that of acoustics 



