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phlogiston had weight

An example of a historical scientific idea now considered an alternative conception:

"The experimenter [Henry Cavendish] now brought a lighted taper to his six samples of gas. He watched each specimen of gas burn with the same pale blue flame. Strange that the same gas should be evolved in each easel What else could this inflammable air be, but that elusive phlogiston? For had not Becher taught that metals were compounds of phlogiston and some peculiar earths? Surely Cavendish had proved that the gas came, not from the acids or water in the bottles, but from the metals themselves! But he must not announce this until he had investigated further-it would not do to startle the world before he had made certain he was right.

With the crude instruments at his disposal, he passed the gases through drying tubes to free them of all moisture, and then he weighed the pure imprisoned 'phlogiston'. Though extremely light he found it actually had weight. It was ponderable. He had nailed phlogiston itself! Now, at the age of thirty-five, he published an account of this work on Factitious Airs in the Transactions of the Royal Society.

Priestley, accepting these results, discussed them with the members of the Lunar Society and the 'Lunatics', as they were called, agreed with him. [Matthew] Boulton especially was enthusiastic, 'We have long talked of phlogiston', he declared, 'without knowing what we talked about, but now that Dr. Priestley brought the matter to light we can pour that element out of one vessel into another. This Goddess of levity can be measured and weighed like other matter'."

Bernard Jaffe (1934) Crucibles. The Lives and Achievements of the Great Chemists. Jarrolds Publishers.

Phlogiston was considered a substance released on burning.

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Referring to phlogiston as the 'Goddess of levity' was to use a metaphor.

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Many examples of science metaphors are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.

phlogiston may sometimes possess the power of levity

An example of a historical scientific idea now considered an alternative conception,

"…Becher would not acknowledge that his phlogiston had failed as an explanation of burning…'my phlogiston may some times possess the power of levity-it weighs less than nothing. Naturally, then, the ash of your metals weighs more than the metals you burned'."

Bernard Jaffe (1934) Crucibles. The Lives and Achievements of the Great Chemists. Jarrolds Publishers.

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tail of a comet ascends away from the sun like smoke that ascends in a chimney by the impulses of the air in which it floats

An example of an analogy used to explain a scientific phenomenon:

"Someone else believes that there can be particles with the property of levity as well as gravity and that the matter of the [comet] tails levitates and trough its levitation ascends away from the sun. But…I suspect that that this ascent arises rather from the rarefaction of the matter of the tails. Smoke ascends in a chimney by the impulses of the air in which it floats. This air rarefied by heat, ascends because of its diminished specific gravity and carries along with it the entangled smoke. Why should the tail of a comet not ascend away from the sun in the same manner?"

Isaac Newton

Isaac Newton (1999) Mathematical Principles of Natural Philosophy (3rd edition, 1726): The authoritative translation (I. Bernard Cohen and Anne Whitman), University of California Press

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The idea (that Newton ascribes to an unnamed other) that some materials might exert a property of levity (a tendency to ascend), as an inherent quality distinct from gravity, was once quite common.

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levity as a natural force

An historical notion that would now be considered an alternative conception:

"But since we are concerned with natural philosophy rather than manual arts, and are writing about natural rather than manual powers, we concentrate on aspects of gravity, levity, elastic forces, resistance of fluids, and forces of this sort, whether attractive or impulsive."

Newton lists levity as a natural power or force distinct from gravity in the Preface to his Principia.

Isaac Newton (1999) Mathematical Principles of Natural Philosophy (3rd edition, 1726): The authoritative translation (I. Bernard Cohen and Anne Whitman), University of California Press.

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phlogiston might have negative weight

An example of an historical idea which would now be considered an alternative conception:

"Somebody suggested that the phlogiston might have negative weight, a positive virtue of 'levity', so that a body actually became heavier after losing it. Such an hypothesis, however, made a serious inroad on the whole doctrine of a solid phlogiston; and we can see that this ancient idea of 'levity' had ceased to be capable of carrying much conviction by the eighteenth century. …. The more popular view seems to have been that while the burning produced a loss of phlogiston and a loss of weight, a secondary and somewhat incidental operation occurred, which more than cancelled the loss of weight.

…it was possible to hold the phlogiston theory and still believe that weight was gained in combustion as a result of something which was taken incidentally from the air this on a sufficient scale to override any reduction that had been produced by the loss of the phlogiston."

Herbert Butterfield (1957) The Origins of Modern Science 1300-1800 (New Edition: Revised and enlarged). G. Bell and Sons Ltd., London.

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worldly matter is composed of four elements

An example of an historical scientific conception:

"As to the ordinary matter of which the earth is composed, it is formed of four elements, and these are graded according to their virtue, their nobility. There is earth, which is the meanest stuff of all, then water, then air and, finally, fire, and this last comes highest in the hierarchy.We do not see these elements in their pure and undiluted form, however the earthy stuff that we handle when we pick up a little soil is a base compound and the fire that we actually see is mixed with earthiness. Of the four elements, earth and water possess gravity; they have a tendency to fall; they can only be at rest at the centre of the universe. Fire and air do not have gravity, but possess the very reverse; they are characterised by levity, an actual tendency to rise, though the atmosphere clings a little to the earth because it is loaded with base mundane impurities. For all the elements have their spheres, and aspire to reach their proper sphere, where they find stability and rest; and when flame, for example, has soared to its own upper region it will be happy and contented, for here it can be still and can most endure."

Herbert Butterfield (1957) The Origins of Modern Science 1300-1800 (New Edition: Revised and enlarged). G. Bell and Sons Ltd., London

Butterfield describes the long lasting notion of there being four elements that comprise (in various combinations) all material in the world (that is, Earth – the heavens were usually considered to be made up of a fifth element, æther). Note that gravity and levity are seen as properties of material objects themselves rather than being seen as relational as in Newtonian mechanics.

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These ideas are anthropomorphic, as they assign to matter characteristics of human personalities – to aspire, to be happy and contented. In modern scienrfic thinking such notions would be seen as pseudo-explanations: you cannot explain motion in terms of what makes flame happy!

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Many examples of anthropomorphism are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.

comet tails contain levitating material

Examples of historical scientific ideas (no longer considered):

"One idea on offer in the seventeenth century was that comets were a matter of levity: the tail was said to be a stream of levitating material subject to a supposed force of anti-gravity that repelled it from the Sun. Or the comet allegedly stirred up the aether in cosmic space like a ship ploughing through the sea."

Nigel Calder (1980) The Comet is Coming! The feverish legacy of Mr Halley. British Broadcasting Corporation

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These days the term 'levity' is used metaphorically, but once it was meant more literally as a kind of opposite of weight.

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The reference to a ship is an analogy that is based on the alternative (historical) conception that space is filled with aether.

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Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.