WALTER G. BOWERMAN has an article entitled "Sunspots in Review" in Sky and Telescope of September, which, although containing nothing new on the subject, provides an excellent summary of research in this particular branch. Much still remains to be done on the effects of sunspots, and in some cases results obtained by different investigators are of a contradictory nature. Thus, while some have discovered that the sun radiates more heat to the earth with increase in the number of sunspots, others have found no such correlation, and additional material is necessary before any definite conclusion can be drawn. H. H. Clayton, writing in World Weather, has pointed out that proof of variation in the sun's radiation with sunspot periods is found in the variation of the polar caps of Mars. When the spots are numerous and at the same time a polar cap is turned towards the sun, it lessens in size. He also states that variations in the light reflected by Jupiter have been found to be associated with sunspot periods. Dr. Stetson, in a letter to Mr. Bowerman, states that evidence from ionospheric investigations reveals an output of solar radiation, especially in the extreme ultra-violet, which is 100–150 per cent greater at sunspot maximum than at minimum. Huntington, writing in "Earth and Sun", suggests that the planets have an influence on sunspots— akin to trigger action—the energy derived from them being like pressing a button to start an explosion. Once a little eddy is started, the slight movement so generated may be reinforced by stresses due to rapid cooling of the sun's outer layer, or to the sun's varying rate of rotation at different latitudes. Mr. Bower-man admits that there are many pitfalls for the student of solar-terrestrial relations, and one must avoid too hasty generalizations. In different parts of the world relationships to temperatures, pressure, and precipitation are not always the same. For example, the Nile shows a maximum height near sunspot maximum, whereas rivers in temperate regions, such as the Parana in the Argentine, show the reverse. Great care is necessary before formulating definite conclusions.