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A recent paper and a preprint both claim records for the lowest carrier concentration at which superconductivity has been observed. However colleagues in Australia and I found evidence for superconductivity at concentrations of the order of at least a hundred times lower in the 1980's, in a ceramic sample of SrTiO_3 with 3% of Ti replaced by Zr., Comment: 2 pages. This will not be submitted as a comment to Phys. Rev. X as they apparently require a large payment from authors

Attention is drawn to the fact that some publications state or imply incorrectly that the BCS-Bose gas transition was first studied by Leggett in 1980, whereas I published a paper on this subject in 1969. Attention is also drawn to evidence from colleagues and myself in the 1980's that a ceramic sample of 3% Zr-doped SrTiO3 was on the Bose-gas side of the transition. This was, I think, the first example of a sample of any material which reached the Bose-gas regime, and also gave a world record by a factor of over one hundred for the lowest carrier concentration (~10^15cm^{-3}) at which superconductivity (or strictly the beginning of a transition) has been observed to occur., Comment: 1 page. Edited version, with the 1989 reference omitted, will appear in Physics Today, February 2005

A simple model is used to analyse published results on large room-temperature diamagnetism for two films of oxidised atactic polypropylene (OAPP) at low magnetic fields. The model involves induced currents expected in circular closed loops of superconductors in fields below the lower critical field H_{c1} at which flux penetration would first occur if a metamagnetic transition did not intervene as in OAPP, and the assumption that resistance would be restored at H_{c1} (negligible pinning). Fits to the data for the more strongly magnetic sample with the model, allowing two different types of loops with different loop radii b_1 and b_2, but with the same cross section a of loop material yield H_{c1} is approximately equal to 5260 Oe, and fits to the data for the less strongly magnetic sample with two loop sizes and with the same value of H_{c1}, combined with the knowledge that the minimum number of closed loops of any type is one, requires that the radius a of the cross section of the material should be less than about 0.8 micrometres, in fair agreement with a maximum radius of 1 micrometre obtained previously from other data., Comment: 9 pages, 1 figure. Journal of Superconductivity: Incorporating Novel Magnetism, to be published