presidext's address. 31 



occurred at aphelion, or at the greatest distance of the sun, must 

 have been subjected to greatly prolonged cold, and under the rule 

 of excessively low temperature, while the opposite hemisphere, 

 with its long summer and short winter, must have been in a 

 condition favorable to most luxuriant vegetation and the support 

 of animal life of ditt'erent form than now existing. This view at 

 all events is based upon naathematic reasoning, and may perhaps 

 account for the geological facts referred to, and the occurrence 

 of successive glacial epochs whose traces are found in comparatively 

 low latitudes. The latest glacial epoch is estimated by Dr. Croll 

 to have taken place 200,000 year.s, but the maximum 840,000 

 years ago. A question here suggests itself, namely, whether 

 epochs of greater or less sun heat, owing to the increase of or 

 diminution of the absorptive influence of the sun's photosphere, as 

 suggested by Professor Langley, may not be also accepted as a 

 probable cause of glacial periods. 



Owing to the| nearness to which the planet Mars often 

 appi'oaches us and the earth-like character of its telescope appear- 

 ance, it natui'ally presents a most interesting study to the 

 astronomer. It is seen to be marked out as if into continents and 

 .seas, the marking often appearing as if obscured by clouds. 

 Very considerable change in the features have been observed from 

 time to time, and recently appearances as of narrow channels or 

 canals have been seen, which have changed and split and been 

 joined by cross channels. These observations have been dilated 

 upon by popular scientilic writers, who have suggested that the 

 canals and channels are the work of martial inhabitants for 

 irrigation or other great engineering purposes. The writers must 

 imagine stupendous works by stupendous beings, when canals 

 and irrigation channels are as wide as tlie Mediterranean Sea. 

 The mapping of Mars has been pushed to a minuteness that many 

 astronomers cannot follow, l)ut the soaring imagination of our 

 popular writer brooks no bounds, and where we have canals and 

 artificial channels this year we may discover barges and steam- 

 boats next. My own experience leads me to regard many of the 

 drawings and speculations concerning the martial surface as 

 being a little in advance of ascertained facts. It is undoubtedly 

 very earth-like in character, and is very probably nearer the 

 same stage (as regards cooling) of our planet than any other, it 

 also appears to be endowed with an atmosphere often cloud-laden, 

 ol)scuring the features of the planet's surface. We wait for 

 increased powers of oljservation at the future near approaches of 

 this planet for further developments. The most interesting fact 

 in connection with this planet is the comparatively recent dis- 

 covery by Hall in 1877 in America of his two satellites, whose 

 existence had not hitherto been ever suspected. The remarkable 

 features of these bodies are their nearness to the parent planet, 

 their smallness, and their rapid motion. They have been named 



