38 



KNOWLEDGE. 



February, 1915. 



in this connection it must be remembered that the great 

 tide-wave which travels along the south coast ol the 

 continent from east to west is retarded by a westerly 

 wind, and its height necessarily increased, and consequently 

 there occurs an additional banking up of the water of the 

 ocean off Cape Leeuwin, which makes its effect felt to a 

 greater or less extent northwards. 



" Thus, when the Moon is in Perigee, the tides are 

 invariably higher and the range greater than in Apogee. 

 This is onlv to be expected, for its attractive force is then 

 at a maximum. So in this respect, at all events, the Fre- 

 mantle tides conform to the generally recognised law. 

 On the other hand, we might expect to find some regular 

 sequence of change existing between the tides and the phases 

 of the Moon, but a comparison between the times and heights 

 of high and low water with the age of the Moon fails to dis- 

 close any existing connection ; in fact, it only still further 

 serves to emphasise the complications present in the tide- 

 governing forces, and to demonstrate the difficulties likely 

 to be met with in an attempt to accurately explain them. 

 For the greatest and least ranges occur both at the change 

 and full of the Moon alike. 



" It should be noted in this comparison that at about 

 the time of first quarter, and again at last quarter, the 

 diurnal tide, namely, one high and one low during the day, 

 is almost invariably in evidence. It also may be taken as 

 a general rule that the highest tides and greatest range 

 occur about the time of Moon's first quarter, although this 

 sometimes breaks down. At the time of full or new Moon 

 the semi-diurnal tides often make their appearance, marked 

 by small range and great irregularity. But it sometimes 

 happens, as mentioned above, that the highest tides and 

 the greatest range take place at these times, with the almost 

 certain prevalence of a diurnal tide. 



" A comparison, however, with the Moon's position in 



declination shows that, when the Moon is on the Equator, 

 the least range occurs, the variation in water-level being 

 about one foot, and also great irregularity in the times of 

 high and low water is apparent. Very little reliance can 

 be placed upon the tidal predictions at this period. Often, 

 for quite a considerable length of time, the water remains 

 unchanged in level. The semi-diurnal tides, namely, 

 two highs and two lows during the twenty-four hours, are 

 also in evidence, but the secondaries are sometimes barely 

 perceptible, the difference between the heights of this 

 inferior high and low water being only a few inches. 



" As the Moon moves north or south of the Equator, 

 the range gradually increases, and the tidal curve becomes 

 regularly diurnal in character. More dependence also may 

 be placed upon the predicted times as the Moon's distance 

 from the Equator increases. 



" Contrary to what might be expected, the highest tide 

 and greatest range happen when the Moon is at its farthest 

 north point, and not at its greatest south declination, when 

 the Moon would be almost directly over Fremantle, and 

 would thus be in a position to exercise the maximum 

 attractive force on the water. 



" It may be stated, therefore, with some degree of cer- 

 tainty, that the Fremantle tides depend to a large extent 

 upon the Moon's declination, and from its position the 

 range of tide may be gauged fairly accurately ; but the 

 irregularity in the occurrence of successive highs and lows, 

 although most marked when the Moon is on the Equator, 

 is still to be expected when the Moon attains her greatest 

 north or south dechnation." 



H. 



The Observatory, 

 Perth, W.A. 



B. CURLEWIS, 



Acting Government Astronomer, 

 Western Australia. 



FLORA SELBORNIENSIS. 



February, Second Month [Continued). 

 22nd. — For the Primrose the Linnean name is used, which still stands at the present day. In 

 a similar way Gilbert White first wrote the name of the Thrush, by which we now 

 know it, but afterwards replaced the specific name by a phrase. He likewise takes out 

 the specific name of the Chaffinch, and corrects the name of the Titmouse from ater to 

 major. The Skylark is now Alauda arvensis. 



March, Third Month. 

 As the Spring is now beginning to come on, the number of entries naturally very much increases. 



3rd. — Torquilla is now the specific name of the Wryneck. The Wood Laurel is Daphne laiireola. The 

 Black Hellebore is Hellehorus foetidns. The Long-tailed Titmouse is now Acredula. 

 Lady-cows are presumably Lady-birds. 



4th. — Chickweed Speedwell is Veronica agrestis. 



5th. — The Common Chickweed [Stellaria media). This plant, with the Common Groundsel and the 

 Veronica just mentioned, are among the plants which may be found in flower during every 

 month in the year. The Missel Thrush is Turdus viscivorus. The Peziza is possibly 

 P. aurantia. 



6th. — The Red Dead Nettle is Laniium purpnreuni. The Common Wren is Anorthuria parvitla. The 

 Clothes Moth is Tinea pellionclla. The Yellow Hammer is now Emheriza citronella. 

 Gctim nrhaniim is the Common Avens ; Wild Cicely, Anihriscus sylvestris ; Herb Gerard, 

 Aegopodium podagraria ; Fool's Parsley, ActJnisa cynapium ; and Goose Grass, Galium 

 aparine. 



7th. — We now call the Wood Lark Lullttla, the Rook Trypanocorax frugilegus, and the Jackdaw 

 Coloeus monedula. 



8th. — The first-mentioned Butterfly is the Brimstone [Gonepterix rhamni), and the others are pre- 

 sumably small Tortoise-shells [Vanessa urtica). We know the Blackbird now as Merula 

 merula). 



9th. — The Hedge Sparrow is Accentor modularis. Dog's Mercury we call Mercurialis percnnis. The 

 Wood Strawberry is Fragaria vesca. The Ringdove is Columba palumbus. There 

 is an interesting observation with regard to the Field Cricket [Grylliis campestris) . 



10th. — Wormwood is now Artemisia absinthium. 



