482 



♦ KNOWLEDGE 



[Dec. 22, 1882. 



r»'seiulilanco to a white dove — tho syinl>ol of tlie Holy 

 iJhost For that reason tlie riower is also known in that 

 country as " Flora el J«pirito .Santo." Tho flower repre- 

 sented in tlie cut was in bloom in the garden of Mr. L. 

 M. Stone, 482, Franklin-avenue, Brooklyn, a short time 

 ago. — .^cifHlijic A iiit-rii-tiu. 



FORESTS AXD CLIMATE. 



i PAPER has been preparetl by Dr. SehomV.urs-k, the 

 ^ 1. liireotor of the I'.otanical Gardens at Adelaide, on 

 the induonce of forests on climate. The object of the 

 author is to prove that tlie destruction of forests usually 

 h&s the eftect of re<lucing the rainfall, while, on the con- 

 trary, the planting of trees broadcast over a country is one 

 of the best methods which can be adopted for ameliorating 

 its climate and increasing the annual fall of rain. It 

 cannot, indeed, be proved that the climate of South Aus- 

 tralia is altering for the worse in this respect. In fact, a 

 comparison of the met<^'orologioal records will show that 

 the annual average rainfall for the colony during the past 

 ten years has been 21-1 in., as compared with 20-1 in. for 

 the previous ten years. The fact is that in the agricul- 

 tural districts of the colony, and especially in those which 

 were not originally timbered, the bringing of the land 

 into cultivation has had the effect of slightly favour- 

 ing the fall of rain. Ploughed land attracts moisture 

 to a much greater degree than the unliroken soil. 

 In considering the effect which the removal of forests 

 yxT *<• has in altering the climate in South Australia, 

 the only direct test that could be taken from the records 

 issued by the Government astronomer is the experience of 

 the neighbourhood of Adelaide. If the time is divided 

 which has elapsed since 1839 — the year in which observa- 

 tions were commenced — into two periods, there is found 

 for the first an average rainfall of 22 S in., and for the 

 second one of 21-7 in. It will thus be seen that, on 

 the whole, the rainfall at Adelaide is diminishing, though 

 very slightly, and perhaps the diminution in tho amount 

 of timber may have something to do with the change. 

 Dr. Schomburgk, in searching for illustrations of the 

 effect of trees on climate, goes further alield, and brings 

 forward some striking instances, in which it is evident that 

 loss of forests means loss of rainfall, and rice vrsd. He 

 recall-s how the Russians, by burning down some of tho 

 Transcaucasian forests at the time of the struggle with 

 the Circassians, converted the country from a fertile 

 land into a desert, simply through the cutting off 

 of the supply of rain. Similar instances of rain having 

 desf!rted a country denuded of forests have occurred in th(^ 

 Mauritius, in Jamaica, tho Azores, and, it may also bo 

 added, to a still more remarkable extent in several of the 

 smaller West India islamls. No sooner had the forests of 

 these places been destroyed than the springs and rivulets 

 ceased to flow, the rainfall became irregular, and even the 

 deposition of dew was almost entirely checked. On the 

 other hand, it is generally accepted as a fact, that Mehemet 

 Ali increased the fertility of Egypt enormously by the 

 planting of trees. He alone plant.!d some 20,000,000 on 

 the Delta ; his succo.ssors followed up the work, and it is a 

 not<5worthy circumstance that the rainfall rose from G in. 

 to 40 in. Planting has also, it would seem, produced re- 

 markable effects in France and Algiers. Ext<;nsivo regions 

 have »<een plant'id with gum and other trees, which, for the 

 raoUpart, grew to aViout .30 ft. or 40 ft in height, and it is 

 mticod that the quantities of rain and dew which now fall 

 on the adjacent land are double what they formerly were. 

 —ArehiUct. 



LUMINOUS PAINT. 

 Bv W. H. Hyatt. 



(^Lecturer on Lv 



raint— Crystal Valnce.) 



V^IONGST the many valuable applications of science 

 to the wants of mankind, few will exceed in interest 

 the composition now known as " Balniain's Luminous 

 Paint." The suliject of luminosity has engrossed the minds 

 of many scientilic men since Casciorolo, of Bologna, in 

 1002, accidentally discovered that by roasting heavy spar 

 in a furnace, a sulistance was obtained which had the pro- 

 perty of giving off light, after having been previously 

 exposed to daylight. This substance is what is now known 

 as sulphide of barium. Since that time, it has been dis- 

 covered that tho sulphides of calcium and strontium, 

 besides many other compounds, possess this remarkable 

 propertj', which has been termed phosphorescence, or by 

 many, " Fluorescence," as conveying a separate meaning, 

 though the two are nearly, if not quite, identical. 



The late Mr. Balmain studied this subject for forty 

 years. At the end of that time, ho patented, and brought 

 out as a paint, a pr(>paration containing rather more oxygon 

 than a sulphide, though not sufficient to form a sulphate. 

 When an article painted with this luminous paint is passed 

 before the spectrum, no fluorescence appears till it roaches 

 tho green, tho violet, and tho ultra-violet, or actinic rays. 

 The ultra-violet rays being too short to aflbot the eye, these 

 it absorbs, and gives themodagain in longer waves, which at 

 once become visible, and continue so for many hours. On 

 the contrary, a strong red or yellow ray will take away 

 tho light from an already luminous surface. To speak in 

 simple language, any surface paintcid with luminous paint 

 and exposed to daylight in the daytime, will shine the 

 whole night through, even the longest winter nights. When 

 a bell is struck, literally the whole of the bell is in 

 motion, and gi\es off waves or vibrations of sound ; in 

 exactly a similar man.ier any wave of light, natural or 

 artificial, falling across the surface of this luminous paint, 

 causes the whole of tho molecules of the paint to vibrate, 

 and give off waves or vibrations of light, which continue 

 from twelve to fifteen hours, and in exceptional cases, 

 twenty hours. Life-buoys, mooring-buoys, channel-buoys, _ 

 itc, painted with luminous paint, are distinctly visible, 

 where a white-painted Ituoy is totally obscured. The paint 

 may be used for a thousand difleront purposes, anywhere 

 where white paint is generally <'mployed, under the erro- 

 neous impression that white paint at night is visible, 

 whereas it is perfectly invisible. Heat will increase the 

 luminosity, and intense cold, as in the Arctic regions, will 

 entirely destroy it, though tho luminosity returns when 

 restored to an ordinary temperature. The light given off 

 will not afreet the most sensitive photographic plates ; added 

 to this, a painted board may be carried, as a lantern, into 

 the most dangerous places, as in powder magazines, without 

 fear of explosion. The rapidity with which this paint 

 will store itself with light is truly marvellous. Ten 

 seconds exposure to diffused daylight will cause it to 

 shine for as many hours, though tho more daylight 

 it has, the better the subsequent <;li'ect. The light for the 

 fir.st hour after lx;iiig exposed is violet, owing to the more 

 rapid vibrations being given off ; after that it is white, till 

 it ceases entirely. Nothing but exposure to light is again 

 required to cause it ^o again emit light. This action lasts 

 for months or years, according to the amount of exposure 

 to weather that the paint receivr!S. To speak roughly, it 

 is rather more durable than ordinary ])aint, and continues 

 to act till the paint is either coated with dirt or worn off, 

 as the action is purely mechanical. Tin' jiopularity of this 



