Nov. 4, 1886] 



NATURE 



only do they resemble each other in their physioligical action, 

 hut that their toxic action increases with their molecular weight, 

 as I have shown to be the case with the inorganic elements, 

 where, in each isomorphous group, the toxic action increases 

 with the atomic weight of the elements. 



In conclusion, I would reprint an extract from a paper pub- 

 lished forty years ago: — " A moment's reflection on the pro- 

 blems to be solved will suffice to show that experiments con- 

 ducted with this class (inorganic) of sub-tances are more likely 

 to fu'-ni-h useful results than those made with bodies derived 

 from the animal or vegetable kingdom, although, owing to the 

 striking elTects caused by some of these substances, physiologists 

 have mostly directed their attention to them. By so doing, 

 however, we are employing re agents witli the properties and 

 composition of which we are imperfectly acquainted, to the 

 neglect of those on the nature of which chemistry has already 

 thrown much light, for not only are we better acquainted with 

 the more purely chemical properties of inorganic compounds, 

 hut their relation to heat, electricity, and molecular polarity has 

 been to a considerable extent made out.' Ja-Mcs Blake 



Disinfection by Heat 



I.\ Dr. Parsons's Report on Disinfection by Heat (Nature, 

 vol. xxxiv. p. 5S3) occurs the st.atement : " It appears that there 

 are no tables or formulae in existence by %\hich the degree of 

 humidity of the air corresponding to a given difference between 

 the wet and dry bulb thermometers at these high temperatures 

 can be ascertained." There are both tables and formulae ; but 

 the tables are the numerical values for the formulfe, and such 

 tables are to be found in Balfour Stewart on " Heat," Dixon's 

 " Treatise on Heat," Blanford's "Meteorologist's Vade-mecum," 

 and numerous works on the steam-engine. 



Let the degree of humidity be represented by /( ; vapour- 

 tension at dew-point by .v ; wet-bulb temperature by /, its 

 vapour-tension by f \ dry-bulb temperature by T, its vapour- 

 tension by F ; barometric pressure by /'. Then, the theory of 

 the dew-point gives 



The tables give the vapour-tension, consequently if T, t, .ind b 

 are known, /; can be found. .\t these high temperatures the 

 degree of humidity would probably not be required very accu- 

 rately. If within I or 2 per cent, of accuracy would suffice, the 

 second tenn may be omitted. This results from the fact that 

 the higher the temperature of the air, the nearer is the dew-point 

 to the wet-bulb temperature. 



/ 



The quantity sought then is, h — — . Given T = 299, 299, 

 F 

 nnd 249 ; / = 146, 165, 190 ; and taking F and / in pounds 

 from a table in " Lardner on the Steam-Engine" : — 



h = = -05 ; 



63 



S'S 



/( = = -08 ; 



63 



29 



Here saturation is represented by unity. This is at once a 

 short and simple method of calculating the degree of humidity at 

 these very high temperatures. If the barometrical pressure were 

 observed, and the long second term worked out, the results 

 would not be materially different, but would be something less. 



R. Strachan 



II, OfVbrd Road, London, N., October 25 



The Beetle in Motion 



Much has been written on " the horse in motion." Can any 

 readers of N.ature supply me with references to published 

 matter on the subject of hexapod progression ? 



The few observations I have made m.ay be summed up in a 

 ftw words. I use the letters r and / to signify the right and left 

 legs respectively, and number the limbs from before backwards. 

 When walking rapidly the appearance is as if / i, ;■ 2, and ^3 

 moved forward together simultaneously, alternating with ;- 1, 1 2, 

 .and r3. When the pace is slower it is seen that /l and r2 

 start together and come down at about the same time, some- 



times one sometimes the other being a little the first. Then, 

 lifted almost but apparently not quite at the same time, /3 

 starts. The motion of this leg being somert hat slower, and the 

 limb having further to tr.avel, the foot generally comes to the 

 ground appreciably later than / I or ;■ 2. The general effect is 

 to produce, at the moments of pause between the strides, the 

 position indicated in the figure, which differs considerably from 

 the conventional position delineated by artists who seek to repre- 

 sent the beetle in motion. C. Lloyd Morgan 

 University College, Bristol 



The Astronomical Theory of the Great Ice Age 



In Sir Robert Ball's paper on this subject, which appears in 

 your last number (p. 607), that author states that the calculation 

 given "has convinced him that Mr. CroU's theory affords an 

 adequate explanation of the Ice age." It is more in the hope 

 of obtaining from Sir Robert a statement of the grounds of this 

 conviction than for the purpose of controversy that I write 

 this letter. 



It will of course be conceded that the frost and snow of a single 

 winter, melted off during the following summer, would not pro- 

 duce an Ice age. But, on Sir Robert Ball's figures, the increase 

 of winter cold at the period in question was accompanied by a 

 corresponding and equal increase of summer heat. Wliy, then, 

 should the latter prove insufficient to melt the winter accumula- 

 tion of snow and ice in any locality where it now suffices to 

 melt it ? 



The question is one of the joint result of two opposing forces. 

 Both, under the supposed conditions, are intensified and equally 

 intensified. How does this affect the result ? ilore snow and 

 ice is doubtless formed in the winter, but then more heat is 

 employed in melting it during the ensuing summer. Why, then, 

 was it not melted in any p'ace where it is now melted ? A kind 

 of answer to this question may be extracted from the writings of 

 Mr. CroU, but not, I think, a satisfactory one. I am therefore 

 anxious (in common, I am sure, with many others of your 

 readers) to hear the reply of Sir Robert Ball. 



Llandudno, October 25 W. II. S. Monck 



The Enormous Loss from Ox-Warble 



I VENTURE to solicit your co-operation in making fome points 

 better known in order that farmers may be better able to protect 

 themselves from the enormous loss from warbles on cattle from 

 the bot-fly, positive proof having been furnished that it largely 

 exceeds 2,000,000/. to 3,000,000.'. yearly ! To begin : I appeal 

 to those farmers who have somewhat studied the question to 

 make it clear to those who have not done so that^ tair/i war/i.'e 

 lump has a laroe tnaggot under it, feeding on the juices of the 

 hide or flesh. The>e lumps many call "health lumps" or 

 "thriving bumps," and scan to prefer that their callle s/umU 

 have them. It is readily seen how this serious fallacy has arisen, 

 viz. from the fact that the warble lumps begin to show about 

 Christm.-is (from the growth of the maggot under them), which 

 also happens to be the time thai the cattle receive their most 

 nourishing food, and are then warmly housed or sheltered. But 

 there could be no greater mistake than to think that the swellings 



