Specially revised for "Now Then", Oct 1965.
| Date | Publication | Publisher | Type | Page | |
|---|---|---|---|---|---|
| March 1953 |
|
Astounding Science Fiction, March 1953 | Street & Smith Publications, Inc. | MAGAZINE | 8 |
| August 1953 |
|
Astounding Science Fiction, August 1953 | Atlas Publishing and Distribution Co. Ltd | MAGAZINE | 2 |
| February 1954 |
|
Space Pioneers | World Publishing Co. | Anthology | 102 |
| March 1959 |
|
Space Pioneers | World Publishing Co. | Anthology | 102 |
| March 1962 | Space Pioneers | World Publishing Co. | Anthology | 102 | |
| October 1965 |
|
Now Then | Mayflower-Dell | Collection | 100 |
| 1967 |
|
Space Pioneers | World Publishing Co. | Anthology | 102 |
| June 1968 |
|
Now Then! | Avon | Collection | 113 |
| 1971 |
|
O Planêta dos Robôs | Editorial Bruguera | Collection | |3 |
| October 1971 |
|
Urania #577 | Mondadori | MAGAZINE | 75 |
| July 2012 |
|
Space Pioneers | Literary Licensing | Anthology | 102 |