Westland. — Southern Variable Stars. 50S 



regular as the flow of time we say they are as regular as the earth's rota- 

 tion. If we suppose that stars are sometimes brighter on one side than the 

 other we have a ready explanation of a regular variable star. Stars of the 

 Eta Aquilae type — that is, spectroscopic binaries which do not eclipse one 

 another — can also be explained on this hypothesis, because if they always 

 turn the same face towards one another, as the moon does to the earth, 

 the period of variability must be equal to the period of revolution, just 

 as the spectroscope shows. Notice also that if the periods of rotation 

 were otherwise they would explain an apparently irregular variable. The 

 two brightest sides turned earthwards would produce the extra-bright 

 maxima, and the two darkest sides would in the same circumstances give 

 the extra-dark minima. These would be the two extremes of brightness, 

 and if the rotation periods were very unequal the intermediate values would 

 be irregular both as regards time and brightness. 



No theory of rotation will account for long-period stars which take 

 months to complete their fluctuations. Mira Ceti and several others are 

 known to undergo physical changes, and at the last maximum of this star 

 I saw the hydrogen line of wave-length 4340 bright without any difficulty, 

 although I have only a 4 in. telescope to collect light for my spectroscope. 



The method of magnitude rating consists of comparing the variable with 

 stars situated near it. Charts of the fields surrounding these stars are 

 obtainable, so that identification of the stars is easy, and the magnitude 

 of each comparison star is given. The observer finds it convenient to 

 memorize the stars he makes use of, because the eye loses some of its 

 sensitiveness if it has to leave the telescope and study a chart by lamp- 

 light. But after the observer has looked over the stars of known magnitude 

 his eye is in tune. I use this metaphor purposely, because. the conditions 

 are similar to those of the ear when it has heard certain notes of the scale 

 played : it is able to pick out the intermediate notes. Similarly, the eye 

 can tell the magnitude of a variable whose brightness is intermediate be- 

 tween two stars of known magnitude, provided that care is taken to get 

 the eve into that condition and to let it work under the best circumstances. 



Art. LIII. — The Distribution of Titanium, Phosphorus, and Vanadium in 



Taranaki Ironsand. 



By W. Donovan, M.Sc. 



[Read before the Technological Section of the Wellington Philosophical Society, 



10th November, 1913.] 



The present writer, in the course of an analysis of ironsand from Patea 

 two years ago, found the amount of phosphorus j)resent to be 0-11 per 

 cent. The highest previously recorded percentage of phosphorus in Tara- 

 naki ironsand was 0-039 per cent., returned by Dr. J. S. Maclaurin in 1902 

 from a New Plymouth sand forwarded by Mr. E. M. Smith.* It seemed 

 important to ascertain whether the high result was accidental, or abnormal 

 in any way, or whether the ironsand deposits generally contain more 

 phosphorus than has hitherto been supposed. In view, too, of the fact 

 that the commercial utilization of the sands would seem to depend on the 



* Thirty-sixth Annual Report, Colonial Laboratory, p. 7. 



