230 THE POPULAR SCIENCE MONTHLY. 



that only motion can breed motion, energy means motion ; and that as 

 such its amount is constant, and its presence, behind whatever veil, 

 continuous ; so that it is only properly divisible into two kinds, per- 

 ceptible and imperceptible. 







SKETCH OF PEOFESSOK MAYER. 



AMONG the younger physicists of the country who have done 

 honor to American science by the interest and extent of their 

 original researches, the subject of the present sketch, and of whom 

 we give an excellent portrait this month, holds a distinguished place. 

 Though now only in the prime of his manhood, he has already made 

 many refined and elaborate experimental researches, by which he is 

 widely and favorably known to men of science both in this country 

 and in Europe. 



Alfred Marshall Mayer was born in Baltimore, November 3, 

 1836. His grandfather, Christian Mayer, was descended from an ancient 

 family in the city of Ulm, Wttrteniberg, and came to Baltimore when 

 a young man. Here he made a large fortune in trade with India and 

 Mexico. He was well known in his day for his liberal and elegant 

 hospitality, his extensive reading, profound knowledge of mercantile 

 law, and those marked social and gentlemanly traits that made him 

 a delightful companion. His father was Charles F. Mayer, who was 

 distinguished for his learning, eloquence, and extensive literary cult- 

 ure. He is the nephew of Brantz Mayer, a prominent writer, who is 

 especially known by his various valuable works on Mexico, where he 

 resided for a time as secretary of legation. 



Prof. Mayer was partly educated at St. Mary's College, in Balti- 

 more, which he left at the age of sixteen for a more practical sphere 

 of study. He entered the workshoj) and draughting-room of a me- 

 chanical engineer, where he remained two years, acquiring a knowl- 

 edge of the use of tools, mechanical drawing, the method of con- 

 structing machines, and careful mechanical manipulation. Subse- 

 quently, during two years, he cultivated analytical chemistry by 

 thorough laboratory practice. 



Prof. Mayer has occupied the chair of Physics, with Chemistry 

 and Astronomy, in several colleges, as follows : University of Mary- 

 land, 1856-'58; Westminster College, Missouri, 1859-'61 ; Pennsyl- 

 vania College, Gettysburg, 1865-'67 ; Lehigh University, Bethlehem, 

 Pennsylvania, 1867-"70; and the Stevens Institute of Technology 

 since 1871. In 1863-'64 he studied physics, mathematics, and physi- 

 ology, in the University of Paris. 



Prof. Mayer's first contribution to science was made in 1855, and 



